I had an error about not being able to modify "iptables", which made sense since it wasn't included in Mint 20. Adding a blank "iptables" file fixed this.
Installed that yesterday along your guide and it went like a charm!
Thank you so much - you made my day!!!
Only thing I couldn't achieve (but that's not tied in the installation) is to get the RT Kernel line as the one in the main Grub window instead of the one with the original kernel - maybe someone can tell how to achieve this.
Update: Found the grub customizer - easy to install and does exactly what I wanted
You are both welcomed, always.
Grub customizer is a helpful tool but it messes to much with the grub stuff, never had issues with it though.
That can also be done by editing grub and updating it, but that also has it's risks as any typo will render the PC non bootable.
