This topic can be closed:
I further investigated and found out that sth. NEEDS to be wrong with php session/s.
So I replaced my apache php.ini with the default php.ini and the error went away.
By replacing I was able to login and now everything goes smoothly.
Difference between modified and default php.ini below
< session.auto_start = 0
session.auto_start = 1
1421c1421
< session.cookie_samesite =
session.cookie_samesite = “None”
Martin.