Hi,
there are two versions of RTL8125 in hardware: RTL8125A and 8125B.
The A-version is supported by (newer) kernels if you have no entry with “blacklist 8169” in in /etc/modprobe.d/
The B-version is supported by kernel 5.9 if you have no entry with “blacklist 8169” in in /etc/modprobe.d/
as the driver r8168 contains the driver r8125.
-------------------------------------------------------------ALTERNATIVE----------------------------------------------------------------------
Load driver from:
https://www.realtek.com/en/component/zoo/category/network-interface-controllers-10-100-1000m-gigabit-ethernet-pci-express-software
(entry: GBE Ethernet LINUX driver r8168 for kernel up to 5.6 ) --> (r8125-9.003.05.tar.bz
sudo tar xvf r8125-9.003.05.tar.bz2 -C /usr/src
sudo dkms add -m r8125 -v 9.003.05
sudo dkms build -m r8125 -v 9.003.05
sudo dkms install -m r8125 -v 9.003.05
sudo depmod -a
sudo update-initramfs -u
reboot.
Deinstallation:
sudo modprobe -rfv r8125
sudo dkms remove -m r8125 -v 9.003.05 --all
sudo rm -r /usr/src/r8125-9.003.05
------------------------------------------------------Alternativ-2------------------------------------------------------------------------------------------------
look for: realtek-r8125-dkms_9.003.05-1_amd64.deb (https://pkgs.org/)
and use “debtap” to convert it to manjaro. Errors on installation can be ignored because "ubuntu-things only)
Best: install it twice before you do “sudo update-grub” finally.