There are so many potential causes of this behaviour.
My brother needed to manually change the MHz it operated on to resolve his issues.
If wifi6 works fine for you, can you force that?
Discussion
Tried disabling it entirely (6ghz) but issues persist even with 2.4 and 5, but even wired connection drops
Thats not good. I doubt you are even close to connecting the maximum devices it can handle. Modern routers are ridiculous for that.
I hope its not bad firmware.
Nope not that many devices. Latest firmware too. But I have a hard time believing 2 separate devices from 2 different brands are both faulty 🤔