Yeah, i'm actually trying to find a new sprite sheet right now
Did some research, have you tried the "Better image uploads" addon?
Again, I've never heard of this engine, I just searched their github and this was an issue about images over 260x480 2 years ago. Here's where I found the information:
https://github.com/ScratchAddons/ScratchAddons/pull/2525
This comment section is getting pretty crowded, I opened a KoFi page yesterday - that's a better place for suggestions and discussion: