First thing I would try is the 7.5.0.242n nightly I have posted, there's a number of fixes in there for Android and I've found it quite stable.
Just remember to copy your old keys from rapt.
And use the quick fix I posted - takes out some excess libs not needed in Android reducing the size by about 50Mb.
Can they provide a traceback.txt? It will be in the /android/data/com.game.name folder.
So I managed to find a phone in the house with the proper android version to crash, so yay. The traceback from renpy 7.4.10 is:
(this is after granting permission, and I did check to make sure that permissions were still granted)
I tried the nightly as you mentioned and it initially crashed as well (installed as an update to the previous), but when I checked the traceback, it was giving an error that the temp folder wasn't empty:
Full traceback:
File "renpy/bootstrap.py", line 331, in bootstrap
File "renpy/main.py", line 446, in main
File "renpy/main.py", line 364, in android_searchpath
OSError: [Errno 39] Directory not empty: '/storage/emulated/0/Android/data/com.domain.rewind/files/../../../../Documents/RenPy_Saves/com.domain.rewind/temp'
Deleting the temp folder and restarting the game fixed the crash and the saves are working properly.
I'm sending this build over to a few people who had the problem with the 7.4.10 version and hopefully they'll report success.