I have the exact same issue as well. MBP 2019. An SMC reset solves it temporarily but it's back within a few minutes of browsing, and it's happening across all the browsers. For some reasons, using Safari seems to trigger it but I can't be sure.
Wifi speed on other devices (iOS, Windows, Android) is 100 MBPS whereas on the MBP w Big Sur, it's ~25 at best. Tested both Wifi and wired, but it's the same.
iamprats
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