I tried installing 12.9 again today and had the same results you as you did. In the end, I managed to installed it by performing a clean install of 12.8 with the June NikGapps core and Magisk 20.4. Reboot back into TWRP 3.4 and flash just 12.9 without wipe.Using TWRP 18.104.22.168 isnt working the last build no matter what; clean install with/without gapps/nikapps isntead load launcher, goes to reboot directly.
Edit: same result with Orange recovery.
Flashed v12.7 and all works fine, 12.8 contains and issue with Gestures module.
It has been running without issue so far.
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