With the huge number of immersive survival and other games we all play I don't see too many F2P titles mentioned.
I have to recommend warthunder if you are a flight sim enthusiast or even aviation in general.
An amazing amount of detail and realism work has gone into the WW2ish vehicles in this game. Getting a kill in the simulator battle is on my list of top notch gaming reward experiences.
Highlights:
-flight models based on historic craft such as, Yak, BF109, P-47
-"arcade" battles for quicker play with forgiving aerodynamics and 3rd person
-"realistic" battles with modled aerodynamic but 3rd person
-"simulator" where view it stuck in cockpit
-tanks are an additional game option that have the most realistic tank feel I have seen
-very reasonable business model where getting to the endgame jets might be the only "grind" you feel
-current nations, U.S. German Japan Russian and Britain
Recommendations:
-stick with Russia for tanks and planes to start and learn the ropes
Downsides:
-the U.S. nation teams tend to fly very poorly so unless you are a pro victories are hard to come by
-the tank sim is still a bit buggy
-bombers defenses are easy to circumvent when not in full simulator so they are flying piñata for opponents
-the learning curve for all the air combat maneuvers is steep