So, I've got another problem now. Usually I try to fix them myself but I can't figure out this one.

See, the background number 15 is a volcano one, but this one is particular because it makes the volcano meteors show up (like in level 8-8 from the original NSMB)

When I want to put the background with meteors, for example, in 8-7, another volcano level, I'm just having a huge error message and the app shuts down after that. I tried to fix the problem multiple times but nothing seems to work
Oh, and the same message appears when I want to edit the sound set. The message says something like "you're touching a closed file"

I don't know what to do now, if anyone can help it would be very appreciated ^^. Thank you

based on what i think i know, you should just close and reopen the app? it happens whenever i accidentally close nsmbe, and i try to save and it says something like You cannot edit a closed file or something. Maybe try re-importing the background from a clean rom file?

Oh wow ! It actually worked. I thought it was a real issue with the code of the game but nope !
Thank you for helping me 🙃

No problem!