When to withdraw other faculty applications: conditional offer letter or contract? I've heard one should let search committees know when you've accepted another offer.  What is the right time to do that?
If I have an offer letter that is conditional on getting a work visa (which I think should be no problem), and I accept this offer, should I wait until I actually sign the contract?
This would probably mean putting several departments through the entire interview process with almost no chance of my actually accepting an offer.
Normally you should not withdraw your applications until you have received a binding job offer that you intend to sign.  If you are delaying signing it, that does not matter.
Depending on your circumstances, an offer conditional on a visa may be extremely risky.  Visa risk is unusually high right now owing to the pandemic, but even before the pandemic I have known people to wait for more than a year for a visa.