One of the best games out rn that is available on almost all OS (works on Linux via WINE or equivalent 'run free Windows apps on Linux' type of software
Legends of Runeterra. At first it appears to be based on luck, do not let this delude you. I play poker and other such games, I know how to interpret luck vs skill in a game; this game involves ~85% skill and ~15% luck. The skill is everything combined; how to build a deck, how to use the deck, how to predict and bait the enemy into misplaying their spells and/or units.
There's levels to this shit, spells that can and can't be used in reaction to others due to spell-type and such interactions. It is fascinating and extremely high skillcap.
In the earlier seasons, it was disgusting how OP some broken decks were but they have genuinely balanced it over time in my opinion. It's also genuinely free-to-play. You can garner the rewards required to unlock superior decks within 1-2 weeks of solid gameplay. I would say if you dedicate your free time to this game that in 3 weeks you will easily have enough rewards to pivot around each other and experiment with in 2-3 entirely different branches. Do not buy cards impulsively, think a little. Cheaper cards will come free in rewards much more often so save green essence for extreme scenarios where you want to push past your wild card max to unlock something.
Avoid going on expeditions and the lab+gauntlet at first. Stick to the main game mode and mix it up with vs AI and vs players. Be sure to do 'challenges' to grasp mechanics of most deck types.