I've had this 2018 Mac mini in the same location for over three years and never had any wi-fi issues, until yesterday when 5GHz started failing. After a lot of testing I found it was working fine with all other devices around the house, except this mini. As a further test I've just pulled an old 2012 mini out of a cupboard and that connected to 5GHz wi-fi in the same room with no problem at all.
From the same router I'm having no difficulty connecting to 2.4Ghz on this 2018 mini, but when I try to connect to 5GHz wi-fi a message pops up saying it could not be joined, yet the iPhone nearby is fine. I've tried removing all the peripherals to no avail, then reset the SMC and NVRAM, but this has been consistent now for about 24 hours. I don't think it is the router, because other devices are OK.
It's starting to feel like this is a hardware issue on the 2018 mini, unless Sonoma is the culprit or somebody knows of another way to troubleshoot this. It seems strange that the wi-fi might fail partially like this, while still working in 2.4Ghz.
From the same router I'm having no difficulty connecting to 2.4Ghz on this 2018 mini, but when I try to connect to 5GHz wi-fi a message pops up saying it could not be joined, yet the iPhone nearby is fine. I've tried removing all the peripherals to no avail, then reset the SMC and NVRAM, but this has been consistent now for about 24 hours. I don't think it is the router, because other devices are OK.
It's starting to feel like this is a hardware issue on the 2018 mini, unless Sonoma is the culprit or somebody knows of another way to troubleshoot this. It seems strange that the wi-fi might fail partially like this, while still working in 2.4Ghz.