Clamshell mode issue

I have a 2020 MacBook Pro M1 Chip with 16Gb Memory. I also have a monitor (asus mx38vc). When I bought the two they worked perfectly in clamshell mode. About a week ago this changed, the monitor shows "USB C no input" when i close the MacBook. It does work as an extension when the laptop is opened though.

I am running MacOS Big Sur 11.4.

I have chatted with the support for over 2 hours and was so far unsuccessful.

Here are things I have tried:

I cannot find the "Energy saver" setting, it doesn't exist on my computer.

I tried the power adapter thing where you dont let the computer sleep when you close it.

I have tried to reset SMC and NVRAM and PRAM (which, after I did it, it turns out don't work for M1).

I have factory reset my monitor. I have shut down and restarted my macbook itself countless times.

I have changed cables (they are connected via USB c cable).

I have created another User with Admin rights to see if it was a user issue.

None of these solved my problem - when I close the lid of my Mac, the monitor turns off and says there is no input.

Thank you very much for any tips and help.