Following up… we just had a real “cable” installed. These experts have devices to check for frequency interference. They said:

The 2.4 MHz frequency is like the 101 freeway; everyone is on it. That’s why the microwave interferes with Bluetooth. 5G much less. These guys argue with customers all the time on router house placements even after they show signals not working.

Oh, they too know it’s not their “cable” everyone talks about “cutting”.

It was nice to talk with real cable guys, and get real internet — but the same shielding to keep Bluetooth speakers playing while heating coffee will also harm the WiFi reception.

Just put the cable back:-)