I think Speed Freeks is still free. Orks vs Orks combat racing game. I haven't played in a couple months so IDK what direction its taking but last time I dropped into a game it was fun as fuck.

Some of them, minus mobile and card games:

1. Speed Freeks - some kind of racing game with orks
2. Rogue Trader - There's two recruitable marines but you can just skip them
3. Darktide - no marines
4. Shootas Blood & Teef - platformer/shooter with orks
5. Inquisitor: Martyr - hack&slash with playable inquisitor, assassin, techpriest, psyker and battle sister in DLC.
6. Two games from Necromunda, seems like multi shooters so i'm not very interested
7. Mechanicus - one of my favourite games from entire 40k franchise, x-com genre strategy with roguelike elements, great immersion
8. Battlefleet Gothic 1 and 2 - ok that's cheating since it's basically RTS, but in space and you can skip marines entirely since they are only subfaction. 2 have Imperium, Chaos, Tyranids and Necron full campaigns. Skallgrim mod on moddb is mandatory it triples the amount of ships including some really huge ones, and it have submods allowing recruiting ork ships for chaos (and Eldar or Tau for Imperium)
9. Battlesector - campaign is marines only but in other modes you can play every faction, there are Tyranids, Orks, Necron, Sisters and Khorne demons (some in DLC)
10. Gladius - underfucked and pale civilisation 40k, but it have a lot of factions. Not recommended though, game is very shallow.
11. Battle sister, VR only and another shooter? Idk, writing this line is more interest than it will get from me ever
12. Armageddon, one of the better strategies from 40k, it has DLC campaign where you play as orks
13. Dakka squadron - aerial shooter with orks
14. Fire Warrior - quite fun but old fps, afaik only game you play as Tau. As a bonus there is a very fun book written on a base of that game, when the writer in a true spirit of old warhammer don't do the thing with toning down the epicness that is always the case when book are written on base of games, but in the book the lone novice Fire Warrior tear a second asshole into everything imperium and chaos throw at him.
15. Rites of War: old as fuck but still one of the best games in genre, you play as Asuryani
16. Final Liberation - only game on a base of epic scale and damn good one at that, but also old enough to make playing pretty painful because it hates your mouse