I have 2 SIMs as well and its working coz the ringtones are stored into the same folder and the permissions are corrected.
e.g. there was in issue in older rom-versions (themes) it should be already fixed from xiomi (I use the default theme)
Did you click on SIM2 instead of "use SIM1" ringtone ?
The permissions of "/data/system/theme_magic" is the issue.
So you have to delete the folder "theme_magic" (the TWRP Module will do it for you)
The folder will be recreated if you select a
new ringtone
Then you will have these files in the folder "/data/system/theme_magic/ringtones"
- ringtone_slot_1.mp3
- ringtone_slot_2.mp3
View attachment 37415
If you have any issues you can use the magisk module: