I had the problem, that the bcmwl-kernel-source broke after updating my upbuntu to the kernel 5.8.0-36-generic #40~20.04.1-Ubuntu. Same as the Question bcmwl-kernel-source-broken-on-kernel-5-8-0-34-generic.
The fix from the answer worked for me. Thanks to Pilot6.
Answer Install bcmwl-kernel-source from groovy repos. You can find it e.g. here. http://mirrors.kernel.org/ubuntu/pool/restricted/b/bcmwl/bcmwl-kernel-source_6.30.223.271+bdcom-0ubuntu7_amd64.deb It will compile with the 5.8 kernel.
sudo dpkg -i bcmwl-kernel-source_6.30.223.271+bdcom-0ubuntu7_amd64.deb
Question Now does the WIFI kernel break again with the next Kernel update? Do i need to manual install the kernel source on every update again?
Or is it somehow possible to prevent such breaks? Since I'm using the Ubuntu 20.04 LTS I didn't expected such error's.