The only issue I was able to resolve was the missing fingerprint functionality: I had to upgrade to the very latest stock fw (POTTER_RETAIL_8.1.0_OPSS28.85-17-6), then PE 11 would recognize the FP reader too.
However, I'm still unable to encrypt the device under PE 11. If I try I always end up stuck at the boot animation. The way to fix this then is booting to TWRP and trigger "Fix Contexts" under "Advanced".
Whenever I flash the stock FW the encryption is active and working, but as soon as I flash PE 11 (or 10) I have to format /data and then can't re-encrypt it.
I've given up for now as my employer for now accepts Android 8.1 on devices with company profiles, so ATM things are ok. But I do miss the new UI and the gestures from Android 11 that's running on my other devices, tho...