They're only expensive if you're buying them day one with DLC. There are lots of ways to save on PC games. There's constant Steam sales, third party key sellers like GreenManGaming (which btw you can get good discounts on new titles through GreenMan) buying Humble Bundles which also supports charity in turn.
The majority of games can be played offline. If you only play multiplayer yeah you're gonna get shafted, but there's loads of amazing single player games, many of which defined the previous decade of one of greatness.
Uhh...yeah? Like the majority of games are still like that only the major live service multiplayer games are like how you described. When you venture out of just the high profile games like Call of Duty you will be introduced to so many amazing games.
If you have a Meta Quest or a PSVR 2 there's one poker game that is completely free to play called Vegas Infinite, formerly known as PokerStars VR. It also supports other casino games like Craps and Blackjack. I've been playing it for 4 years ever since I got into VR and I guarantee you'd love the game. On Windows it has a 2D mode if you don't got a headset, but honestly the game is meant to be played in VR due to it's immersion. Actually being face to face with the different people you play online poker with, socializing with them, some being across the otherside of the world, and being in a poker table having a virtual martini in Macau in the far future or on a yacht in Monte Carlo. It's a unique experience you gotta try.
Alright back to the recommendations. If you want milsim and space flight Mac games specifically that number is gonna be small, but I'm sure you already know that. ARMA 3 is on Mac, and was updated for native Apple Silicon support recently. If you want a milsim, ARMA 3 is your game
For Space Flight, the highly popular and multiple award winning space sandbox game No Man's Sky got a Mac port this year.
Annnnnd that's it. That's all I got unfortunately that you requested. If you want other genres or games on Windows and Linux I can help with that but space sims on macOS is pretty much just EVE Online (which is a MMO that requires a subscription and has an additional money and time sink that don't even get me started on that) and No Man's Sky.