This "should" be able to unlock the gallery. I am still trying to work out what is going on with the saves. Put this wherever your game is being saved. I am doing this on a mac so the path for me is /Users/*****/Library/Application Support/com.DefaultCompany.2D-URP - I suspect the saves going here by default could be some of the issue. I am not familiar with unity, I am a dev but for embedded systems but I did look up what that path is sometimes used for and normally this would be for rendering pipeline specific features. Any unity devs please correct me if I am wrong. Anyway give this a try for now if you want.
Also if your saves are working I would not use this as i did not do any testing I only ran it after making changes and I don't know what side effects this may have...
I am not sure if the dev comes here often but if you do, just a suggestion but I would check out some of the libraries that are available for unity saves. SaveGameFree looks like a pretty good one that is available on github(Again not a unity dev). You have a good game here so it might be worth it to take a look at some of these. Refactoring can be a pain in the ass but it can make your life much easier in the long run. Just my 2 cents, I know much more goes into this than most people will ever realize.
Also if your saves are working I would not use this as i did not do any testing I only ran it after making changes and I don't know what side effects this may have...
I am not sure if the dev comes here often but if you do, just a suggestion but I would check out some of the libraries that are available for unity saves. SaveGameFree looks like a pretty good one that is available on github(Again not a unity dev). You have a good game here so it might be worth it to take a look at some of these. Refactoring can be a pain in the ass but it can make your life much easier in the long run. Just my 2 cents, I know much more goes into this than most people will ever realize.