Hi @Tret ,
according to your problem, please refer to the following FAQ to try to troubleshoot your Wi-Fi problem first.
Also, I have PM you for confirming Wi-Fi issue details.
Could you please check the PM inbox at the top right corner of the screen and kindly provide the requested information?
I have faced the same problem with my ROG PHONE 5S, after updating wifi stopped working.
On day one, ASUS Service Center(F1 Lajpat Nagar) in NEW DELHI denied the support by blaming the 3rd party apps. On day two after formatting wifi stopped working after a few minutes, and they submitted the device for observation without any sure shot ETA. As usual pretty poor service experience of ASUS. Time to move on...
RMA No. - ING2R60***.