Here is my output (as already recomended in this thread):
sudo update-initramfs -u -k all
update-initramfs: Generating /boot/initrd.img-5.9.0-5-amd64
update-initramfs: Generating /boot/initrd.img-5.9.0-4-amd64
W: Possible missing firmware /lib/firmware/ …
I mean under (perhaps) /lib/firmware/rtlwifi/ in accordance with this post (last one) and this link (if corresponding to your WiFi card).
To be sure which WiFi card is built-in, from this orientation link: HowToIdentifyADevice/PCI - Debian Wiki, you might execute:
sudo lspci -nn | grep Network
As well you might edit/add this repo (with or without main) to your sources.list as described here:
by adjusting/including above post up to this Debian link here with non-free.