After my GF got the Android 11 Update from Sony for her Xperia 10 II, the Phone became really buggy. Freezes, no mobile Internet and so on. After hours of working, i made an .ftf File to flash back to Android 10.
You need to unlock your bootloader to flash. i used the actual Flashtool for MacOs to flash.
Use it and fall again in love with your Xperia
※Please make a backup of your device before installing or updating ROM