k20 pro too , I using 10.3.12 with magisk for tasker greentify and nfc simulator without bug. I always flash magisk uninstaller before update new eu rom, and then flash magisk again, may be you can try :D
go to setting -> system app-> you wil see "google service" in that, just enable it and install google play store then , k20 pro come with builtin google play service but not enable, just enable it
with k20pro i don't have yours problem but I have too much other problems (crash, app not work etc....) too and this is what i did and now i don't have any issue , may be you can try:
_ Backup your data
_Wipe all
_Use MiFlash flash again miui china 10.3.8.0 ...
forget about bat files
just go fastboot and flash recovery and misc (remember rename twrp img for your command) :
1.
fastboot flash recovery recovery.img
2.
fastboot flash misc misc.bin
may be they restored localbackup
I clean install all and work perfect!
btw, some apps not work normal or crashed when restore from localbackup,clear data not resolve,only uninstall and reinstall can make them work! (sorry about my bad English)