Great.
Works under OTA-24 on FairPhone 3+.
Saves me from taking notes during a call.

Here is what I was talking about .
After copying photographs for this post, I reconnected FP3+ and restarted ubports-installer (root session). Meanwhile I started writing this post (user session). After some time FP3+ came up with Ubuntu Touch. No idea what did it.
Differences from before:

1. FP3+ was disconnected/reconnected (same usb2 port). Meanwhile another phone had been connected to this port.
2. UBports-installer was run twice.

Glad that I can now discover UbuntuTouch.
Thanks to all who helped. Vielen dank für die Hilfe
Rudy

@luksus said in FPOS Android 10 download WANTED:

• did you check "wipe userdata" in ubports-installer?
  <Yes
• You could try to run the ubports-installer again.
  <Already tried
  ubports-installer (nice tool) offers me three flavours of 16.04/arm64/android9. Tried 'stable'.
  There UBports complains (FP3+ screen with UBports-installer-logo) "Can't load Android system"

@3r853n & @luksus : Found all information and files (thanks).
Started from FP3+ and Android 11.
After flashing Android 10 (md5 checked and correct) FP3+ reported "Can't load Android system".
Tried UBports-installer, same result. Cleaned Cache and Date with TWRP and flashed again. Same result. Back to Android 11 same result.
Something broke in the first step?
Any suggestions?

Alas. Neither of the links to a stable FPOS Android 10 here above still refers to the needed software. As Halium 10 is advised for FP3+ and should be loaded over FPOS Android 10 this would lead to a nogo for ubuntu on FP3+.
Does anyone know:

• What I would loose if I install Halium 10 or 11 over FPOS Android 11 on FP3+?

Running FPOS Android 11 on FP3+.
Want to try Halium 10, which is to be installed from (Fairphone OS) FPOS Android 10.
FP does not provide older versions, which I understand.
Where can I find a stable Android 10 for FP3+ ?

@w_m0zartUBports: Thank you, will give it a try.

FP3+ is upgraded to android 11.
Halium 10 does not support android 11.
Halium 11 does not support FP3(+).
What version to try?