Hi everybody, thanks for the help so far. Although the suggestions listed above didnt work for me, i think I found a new workaround.
Problem: Same wifi connected -> disconnected -> connecting loop as everybody but it happened on two separate mobile devices. The devices connection still works with other wifis though, even hotspots.
Ive tried: restarting/rebooting devices and router, clearing cache. Even replacing router and assigning a static IP-Address didnt work.
My workaround: In router settings, I assigned a guest-wifi hosted by the same router. picked a random password and boom, connection is stable.
I am really confused as to why this works, so if somebody understands please let me know. I am not sure if this is a long-term solution, as my devices used to work with the original wifi for some time before they started disconnecting more often until they were in a complete loop. Cheers everybody