Comment 3 for bug 1890641

I had also the Prblem with the missing of /lib/firmware/rtl_nic/rtl8125a-3.fw
Then i have found the rtl8125a-3.fw on git
https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/tree/rtl_nic
then download and copy in the directory /lib/firmware/rtl_nic/
and the command
$ sudo update-initramfs -u
update-initramfs: Generating /boot/initrd.img-5.4.0-42-generic

reboot and all is ok