Control: close -1 5.10.24-1 I recheck the situation with Debian kernel 5.10.24 and Debian firmware-brcm80211 20201218-3. 5GHz WiFi works fine with vc4 and without vc4.
Debian package of firmware-brcm80211 newer than 20201218-3 has a severe issue with 5GHz WiFi as reported at https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=984489 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=985632 But it is a separate topic. Best regards, Ryutaroh