Don’t know what happend, after I changed 150 mbit/s to 300 mbit/s, now I suddently have faster network, my main router says actually 270/122 and speedtest by Ookla is also fine:

Looks kinda like he router had problems to change to 300 mbit/s and maybe was stuck in 11 mbit/s mode some how.
Thanks for your help!
Now when I look at the WIFI app, both network uses the same channel.