flushing the cache of my browser was the solution.
After that i could use my known login and password and it worked!

i have a rpi 3 with the domoticz software. I accidentially updated to the latest version with a aeotec z-stick gen 5 which doesn't work anymore. So i want to restore a selfmade SD backup from version 2023 When the domoticz software starts up for the first time, ik must login with user and password ...