Do you have any experience in using Tabletop Simulator software in Ars Magica? Maybe anybody made custom table for it? This can be solution for lonely masters/players...
Tabletop sim is, in my experience, not the ideal format for online rpgs. For one, everyone has to purchase the game, and be able to run it smoothly (not guaranteed, my laptop chugs when trying to run TS). For another, it can be a little fiddly and it's no fun when you end up spending as much time trying to get the physics to behave as playing the actual game. It can also be distracting with people playing around with the simulator itself rather than focusing on the rpg. Not sure about any Ars specific resources for it.
The one upside is if you really, really want to use miniatures in your game it's as close as you'll get without an in person session.
For online play I'd recommend a more rpg oriented virtual tabletop like Roll20 (others exist, but I use Roll20 so it's the example I'm most familiar with). It's free (with some ads), it's simpler to use and get assets for (image tokens instead of 3d models), and all you need to use it is a computer of some kind. In the case of Roll20 specifically there are forums to advertise and look for games and a very nicely (fan)made built in character sheet for Ars 5e.
Roll20 for the tabletop and Discord for voice is how I play all of my rpgs these days.
Argentius, I guess you play in english?
Just to know, because i'm wondering if there are as big communities on these online platforms in other languages. (From my experience, no.)
Considering that ArM is a fairly niche game with a small population compared to say D&D or even GURPS and Fate, we are not numerous enough to sustain active parallel non English speaking communities.
There is some community extensions, more or less precise from the rules point of view, running on Fantasy Grounds.