In the meantime you can give a look to the Servo project. If Servo is clean for you, you can support them.

Is Librewolf already a Firefox without ad companies colonization ?

Is the web engine an issue about privacy ? Or are these things implemented in front ends instead ? Sorry for my ignorance.

Is it possible to make it working on a today machine ? Even with a virtual machine ? Sorry for my ignorance.

I switched two times. WinXP to Mandriva, because of devastating rootkits. Win8.1 to Mint because of performance decrease.

I like simple default, so it is easier to customize. But If I have to keep the default I would say Garuda.

This is unrealistic. Read everything represents too much work.

If you want stability you can choose Xfce. You’ll don’t need extensions because of easy configurability.

Is Guix a cleaner base for a NixOS alternative ?

Maybe MX attracts people who just want to use their computer easily. They are not interested in talking about their OS on the web.