Can you upload an appendix externally for referencing? I am submitting an article to an IEEE transactions journal with a strict page limit. We have already scrapped heaps of text, but can't shorten the appendix (or do without) since this would prevent reproducibility.

We have tried uploading the appendix as supplementary material, but this was not approved. Is there a way to upload the material externally for referencing? Or is this not done in academia?

Kind regards,

Ties
I routinely use the Open Science platform (see https://osf.io/) for things like model code, simulation results, data dictionaries, supplementary figures and all the other extraneous materials that are needed for reproducing results. I haven't submitted to IEEE but I have had no problem with any of the journals I do submit to.

The way it works is that you upload the material and create a registration (a snapshot or archive) which is public and cannot be changed. I typically leave the project open until the final draft and then create the registration. That registration will have a URL which I then include in the edits.

There are many such repositories, some field specific. Nature has a list of places for archiving data at https://www.nature.com/sdata/policies/repositories with comments about what can be stored there.