Dirty flash done!
I cleared the caches by TWRP and rebooted.
It's a beauty (but I'm still testing!). ;)
To install *no-support-for-this-app-on-this-forum* I had to redo the procedure:
Install Magisk 17.1 stable (through TWRP);
Install the build.prop app and activate (api2) by adding the line "persist.camera.HAL3.enabled=1"...