Found a solution using the Wi-Fi repeater (now with a different SSID) only for the iMac... Everything's back to normal. The absurd is that before Big Sur I never experienced those problems.

Recent OS update 11.2.1 didn't fix this bug... Seems that my iMac switch from my router to the wifi repeater and back (Same SSID). If you have a repeater try unplugging it; connection is WAY worst, but no more dropping connection.

Recent OS update 11.2 didn't fix this bug...

After upgrading to 11.1 from Catalina, Wi-Fi became unusable on my late 2014 iMac 5K. At first I tought was my router... (never had any kind of problem before) after some tests, ended that the problem was the OS upgrade. Connection drops frequently, ping goes high and low. Online conferencing, gaming and Stadia totally unusable; via Chromecast is perfect. Really hope tha 11.2 fix this terrible bug...

After upgrading to 11.1 from Catalina, Wi-Fi became unusable on my late 2014 iMac 5K. At first I tought was my router... (never had any kind of problem before) after some tests, ended that the problem was the OS upgrade. Connection drops frequently, ping goes high and low. Online conferencing, gaming and Stadia totally unusable; via Chromecast is perfect. Really hope tha 11.2 fix this terrible bug...