I am on v219 and everything except fingerprint works.
When I flash A15 firmware before installing v219 then there is no option to add fingerprint or face unlock under Settings -> Security.
Could it be that A15 is too new and I need A13? If so where can I get it?
When I flash C25 firmware before installing v219 and I want to enable fingerprint I get the "Touch the sensor" message and it tells me the sensor is at the back of the phone. It also shows a green circle on the screen where the senor actually is but when I touch that nothing happens. Similar to this video:
The latter situation also happens when I use lineageOS. Other users in the lineageOS thread describe the same problem.
I solved it, this is what I had to do:
I clean flashed colorOS, booted it up and had exactly the same issue with the fingerprint still not working.
I then made sure that colorOS had replaced twrp with stock recovery so I could safely lock the bootloader without bricking the phone. For anybody trying this I cannot stretch enough how important this is! If you lock the bootloader with twrp installed you will brick your phone and with the limited developer support out there you will struggle to find instructions for edl flash which is what you will need in that case!
After locking the bootloader the fingerprint started working in colorOS.
After unlocking it again the fingerprint reader continued to work in colorOS.
Then I simply followed the instructions in this thread and now fingerprint works in LOS as well.
To clean flash colorOS (or realmeUI) boot into twrp, wipe data, adb push the ozip (see next step) to your sdcard, install it like you would a regular zip file, reboot into recovery (this is important), format data (where you have to type yes; this did not work for me if I didn't reboot into recovery after installing the ozip), reboot into system.
You can download the ozip for realmeUI or colorOS from here: https://realmeupdater.com/
As far as I understand it:
RMX1931 for chinese phones
RMX1931EX for global phones
in the next step the A.XX versions are for colorOS, C.XX are for realmeUI
If you install realmeUI you need a different deeptesting apk to unlock again. It is a bit hard to find with many people telling you it is not possible to unlock realmiUI. Use this apk: https://drive.google.com/file/d/1bdA...IOJGrXpy2/view
You can follow these instructions: https://www.youtube.com/watch?v=WLUffY1_dR4
Many thanks for your help everybody!