Opened score in nightly version, no way to get it back to Musescore 3.6

I had just finished a score, when I decided to download the latest nightly version of Musescore 4 to see what was going on with that. I opened said newly finished score (never uploaded it) in MS4 to see what it was like, before deleting the program and going to MS3 to print it.
Only, the score won't open because it says it's in a newer version of Musescore and can't regress back. I don't remember ever hitting save, so I don't know how this could possibly happen.
I really need this score back, and there's no backup of it anywhere.

Workarounds I tried: mscz, backup file (last save was too long ago to save anything worthwhile); exporting or copy-pasting from the new version (won't work because it crashes every time I try to open that score); uploading the file to musescore.com to redownload (runs into an error on upload)
The last thing I could think of was changing the code of the mscz file manually to accept 3.6 as a version number which I think would work since I don't recall ever saving it in the new version. I'm unfamiliar with how to do this tho, it's a mess in notepad.

Any help would be dearly appreciated, thanks.

I attached the defective mscz file in case someone can fix it and send it back