Nope, still not working. maybe because of interference between the two routers. maybe i will downgrad the firmware.

alright. first it didn't work. same problem: after a few hours the 2.4 ghz wifi would loose connection to router number 2. i said at least i can access the web surface of RE450 through the 5 ghz wifi...

@tblinkarchera5 let's go from this to this using the first router as the default gateway and on of the first routers internal ip-addresses (...73)

Firmwareversion: 1.0.7 Build 20211029 Rel. 57236(6985) Hardwareversion: RE450 v2.0

the picture in this link is also very interesting https://community.tp-link.com/en/home/forum/topic/234794?replyId=621400

i think, i got this solved https://community.tp-link.com/en/home/forum/topic/259906 because one of the repeaters (a cheap one), spreads the wifi directly from the router to RE450 and it simply won't...