user-1: Is there any website which tracks the number of Bitcoin transactions, fees and amounts associated with layer 2 projects (Lightning Network, Liquid, Rootstock)?
I am curious about this because if a sidechain like Liquid doesn't really contribute to some Bitcoin transactions, fees and has different trust assumptions is that helping Bitcoin in anyway?
Will this become difficult to know after enough people start using Taproot? It should be good for privacy but it helps if you know how much a layer 2 project affects layer 1 in different ways.
https://bitcoinkpis.com/layer2 has some information about LN but nothing about transactions.
https://bitcoin.clarkmoody.com/dashboard/ has information about bitcoin locked or used in Liquid but no transactions.
https://explorer.rsk.co/ also mentions bitcoin locked/used.

user47827: 1ml.com has some statistics on the Lightning Network. That includes one statistic on new channels which each require an onchain transaction. It also has a page on closed channels which also require an onchain transaction.

I am curious about this because if a sidechain like Liquid doesn't really contribute to some Bitcoin transactions, fees and has different trust assumptions is that helping Bitcoin in anyway?

If Liquid or any project is providing a use case or meeting a need that is bringing users and additional use cases into the Bitcoin ecosystem without intensive use of the blockchain surely that is good for Bitcoin? Liquid (and other sidechains) do have occasional peg in and peg out onchain transactions and so do provide some fees. But surely we aren't judging what is good for Bitcoin by how much block space it takes up? Otherwise bring back Satoshi Dice :)

Will this become difficult to know after enough people start using Taproot? It should be good for privacy but it helps if you know how much a layer 2 project affects layer 1 in different ways.

Absolutely. That's one of the trade-offs. More privacy for individuals at the expense of some network statistics and some network visibility. Although Lightning and other offchain protocols won't use MuSig and FROST multisig/threshold sig key aggregation schemes immediately post activation of Taproot, once they do it won't be obvious which onchain transactions are supporting offchain protocols.

user5406: I'm not aware of any sites that track all the information you're looking for already, and I know next to nothing about RSK.
Lightning
Transaction data in the Lightning Network is private by design, so while some node operators could publish their own node's payment stats, there cannot ever be a global measurement. As Michael mentioned, every Lightning node learns how many announced channels get opened and closed. It is currently also possible to identify closing of private channels since the Lightning Network is the biggest use case for 2-of-2 multisig transactions by far. Once Taproot activates and channels make use of P2TR outputs for their anchors, only unilateral closes will be identifiable unless there are other indicators.
Liquid
Transaction amounts in Liquid are confidential, but the count of transactions is public. You can find a complete journal for example on https://blockstream.info/liquid. Given that the Liquid federated peg uses 11-of-15 transactions, it should be easy to track down peg-outs, while peg-ins will also become apparent after the output is spent. Since MuSig only works for n-of-n aggregation, spends should remain identifiable even after Taproot activation until an aggregation scheme supporting k-of-n constructions is found, but even then, the Liquid Federation funds may remain traceable, since the Federation uses (at least currently) a fixed change address.

-1: <p>Is there any website which tracks the number of Bitcoin transactions, fees and amounts associated with layer 2 projects (Lightning Network, Liquid, Rootstock)?</p>
<p>I am curious about this because if a sidechain like Liquid doesn't really contribute to some Bitcoin transactions, fees and has different trust assumptions is that helping Bitcoin in anyway?</p>
<p>Will this become difficult to know after enough people start using Taproot? It should be good for privacy but it helps if you know how much a layer 2 project affects layer 1 in different ways.</p>
<p><a href="https://bitcoinkpis.com/layer2" rel="nofollow noreferrer">https://bitcoinkpis.com/layer2</a> has some information about LN but nothing about transactions.</p>
<p><a href="https://bitcoin.clarkmoody.com/dashboard/" rel="nofollow noreferrer">https://bitcoin.clarkmoody.com/dashboard/</a> has information about bitcoin locked or used in Liquid but no transactions.</p>
<p><a href="https://explorer.rsk.co/" rel="nofollow noreferrer">https://explorer.rsk.co/</a> also mentions bitcoin locked/used.</p>
 47827: <p><a href="https://1ml.com/statistics" rel="nofollow noreferrer">1ml.com</a> has some statistics on the Lightning Network. That includes one statistic on new channels which each require an onchain transaction. It also has a page on <a href="https://1ml.com/channel?order=closedchannels" rel="nofollow noreferrer">closed channels</a> which also require an onchain transaction.</p>
<blockquote>
<p>I am curious about this because if a sidechain like Liquid doesn't really contribute to some Bitcoin transactions, fees and has different trust assumptions is that helping Bitcoin in anyway?</p>
</blockquote>
<p>If Liquid or any project is providing a use case or meeting a need that is bringing users and additional use cases into the Bitcoin ecosystem without intensive use of the blockchain surely that is good for Bitcoin? Liquid (and other sidechains) do have occasional peg in and peg out onchain transactions and so do provide some fees. But surely we aren't judging what is good for Bitcoin by how much block space it takes up? Otherwise bring back Satoshi Dice :)</p>
<blockquote>
<p>Will this become difficult to know after enough people start using Taproot? It should be good for privacy but it helps if you know how much a layer 2 project affects layer 1 in different ways.</p>
</blockquote>
<p>Absolutely. That's one of the trade-offs. More privacy for individuals at the expense of some network statistics and some network visibility. Although Lightning and other offchain protocols won't use MuSig and FROST multisig/threshold sig key aggregation schemes immediately post activation of Taproot, once they do it won't be obvious which onchain transactions are supporting offchain protocols.</p>
 5406: <p>I'm not aware of any sites that track all the information you're looking for already, and I know next to nothing about RSK.</p>
<h2>Lightning</h2>
<p>Transaction data in the Lightning Network is private by design, so while some node operators could publish their own node's payment stats, there cannot ever be a global measurement. As Michael <a href="https://bitcoin.stackexchange.com/a/109469/5406">mentioned</a>, every Lightning node learns how many <em>announced</em> channels get opened and closed. It is currently also possible to identify closing of private channels since the Lightning Network is the biggest use case for 2-of-2 multisig transactions by far. Once Taproot activates and channels make use of P2TR outputs for their anchors, only unilateral closes will be identifiable unless there are other indicators.</p>
<h2>Liquid</h2>
<p>Transaction amounts in Liquid are confidential, but the count of transactions is public. You can find a complete journal for example on <a href="https://blockstream.info/liquid" rel="nofollow noreferrer">https://blockstream.info/liquid</a>. Given that the Liquid federated peg uses 11-of-15 transactions, it should be easy to track down peg-outs, while peg-ins will also become apparent after the output is spent. Since MuSig only works for n-of-n aggregation, spends should remain identifiable even after Taproot activation until an aggregation scheme supporting k-of-n constructions is found, but even then, the Liquid Federation funds may remain traceable, since the Federation uses (at least currently) a <a href="https://blockstream.info/address/3EiAcrzq1cELXScc98KeCswGWZaPGceT1d" rel="nofollow noreferrer">fixed change address</a>.</p>
