connected external monitor prevents automatic screen lock

when my laptop (Acer Swift 3 SF314-42, Ryzen 5 with AMD GPU) is connected to an external monitor automatic locking of the screen does no longer since a few weeks (since 22.4.2?). It shows the following behavior.

1. After the set idle time both screen blanks.
2. The builtin screen wakes up again after a second.
3. All windows from the external monitor have moved to the built-in screen. So, it looks like the blanking (suspend?) of the external monitor caused a new display settings (single built-in screen). Maybe that has than woke up the built-in screen.
4. After another second the external monitor also wakes up.
5. Display settings changes to dual screen again.
6. Countdown for idle time resets.
7. Game starts again from (1) after the set idle time.

So, the screen never stays blank and screen never locks.

Not sure if this is the right package to file the bug report.

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: gdm3 42.0-1ubuntu7
ProcVersionSignature: Ubuntu 5.19.0-32.33~22.04.1-generic 5.19.17
Uname: Linux 5.19.0-32-generic x86_64
ApportVersion: 2.20.11-0ubuntu82.3
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Tue Feb 28 01:40:12 2023
InstallationDate: Installed on 2022-05-02 (302 days ago)
InstallationMedia: Ubuntu 22.04 LTS "Jammy Jellyfish" - Release amd64 (20220419)
SourcePackage: gdm3
UpgradeStatus: No upgrade log present (probably fresh install)