Thanks.That's a wrong answer. It can be dirty flashed, but Gapps need to be flashed before first boot.
I did dirty flashed from 15, wipe cache and delvik, restarted and google play crashed then i realised i forgot to flash Gapp
Rebooted to recovery, flashed gapps for android 9, flashed magisk again, rebooted, and all running smoothly now!
Battery has improved dramatically from 15.
Thanks @bgcngm !!!!!