Cette solution ? Le souci est que j'ai peur de faire une conn.... ne maîtrisant pas du tout le souci !!
I managed to restore WiFi with kernel 5.4.0-59-generic as follows:
Purge all packages related to kernel 5.8.0-34-generic: sudo apt purge linux-image-5.8.0-34-generic linux-image-unsigned-5.8.0-34-generic linux-modules-5.8.0-34-generic linux-headers-5.8.0-34-generic
Purge the Broadcom WiFi driver: sudo apt purge bcmwl-kernel-source
Remove redundant packages: sudo apt autoremove
Put the 5.4.0-59-generic kernel on hold: sudo apt-mark hold 5.4.0-59-generic
Update package metadata: sudo apt update
Re-install the driver: sudo apt install bcmwl-kernel-source
Since the 5.8.0-34-generic kernel is gone, the driver is compiled only for the 5.4.0-59-generic kernel which succeeds as expected. Reboot, and WiFi is restored.
Hopefully I can unhold the kernel and receive kernel updates as usual once this is sorted out.
