Thanks for the tips π
Looks like I have/had 2 problems.
First an override of hook.php made by Express Cache 3, which was not installed anymore.
Second Collect PHP Logs v1.1.1, which I had to uninstall.
After removing these 2 issues it was possible for me to update to TB 1.5.0.
But if I tried to re-install Collect PHP Logs v1.1.1 again, then I get server error 500 again.
So Collect PHP Logs v1.1.1 does not work in my environment.
Edit: Found a version Collect PHP Logs v1.3.0 on Github, so the module works now π
BR Elund