FInally I found the time to install 18.1 on my (spare) LG G5.With LOS 17.1 and 18.1 I never seen issue on fingerprint reader, but only on NFC.
In the past Open Gapps was not supported on LOS 18.1(android 11) but only 17.1(android 10) and they worked well. Now I see is supported also on android 11, I think works but I never tried, I'm using Nikgapps and are good.
I never used android auto so I don't know.
I sticked to this "guide" and started with 15.1 and ended with 18.1.
Everything works fine, except of the fingerprint reader, even Android Auto works!
I tried this time MindTheGapps and encountered no problems during the installation.
You are talking about the counterpart of this area on the mainboard, right? (took the screenshot from this video)
I'm still a little bit skeptical, the fingerprint reader stopped working on my two G5s almost at the same time, but it've to be a hardware decet, during flashing 15.1 - 18.1 it never worked.
(By a funny coincidence I've got two H850 and I'm switching them regulary after testing a new / updated rom on the other device)