The obvious answer is CCGs like Yugioh Master Duel, Magic Arena, Pokemon TCG Online, or Hearthstone. But of course those all use predatory monetization mechanics. A fun sorta-competitive strategy game that doesn't have booster packs you buy with cash is Super Auto Pets.

It sounds like you might really like auto-battlers, also called "auto-chess" style games. Auto Chess started as a Dota 2 mod, and now Dota has their own called Underlords. League of Legends also has an auto-battler spinoff; it's called Teamfight Tactics. And don't sleep on the indie Super Auto Pets. It's pure fun.

Action game, but World of Warships, maybe? Game is VERY slow and you don't need reflexes or clicks per second to win, but rather planning and game sense

Probably not entirely your wheelhouse but have you considered coop turned based strategy games (or just turn based in general)? Something like Divinity 2 requires strategy and planning, especially on higher difficulties, but they are entirely turn based and can be played in real time in co-op. Alternatively, games like Disciples Liberation which centers around tactocul turn based combat can be absolutely brutal on high difficulty.

Might be outside of what you're looking for, but have you considered online chess? It's fun to learn, doesn't need quick reflexes, and the playerbase is never going to die.

You might like Total Annihilation and its modern descendants, like BAR or Zero K. There's still some micro depending on the variant, but the focus is much more heavily on macro, along with making the units smarter.

Apart from that, the Civ games are turn-based, but scratch a similar itch as RTS games

Hunt Showdown!

Slow paced extraction shooter, completely without automatic guns.

Tactics and patience win almost always over twitch aiming skills.

it’s definitely outside of your scope, but since when I discovered boardgaming (specifically german boardgames - which are actually not made in germany, it’s just the name of the genre) I got severely hooked into that. these are mainly no-luck deterministic games where you compete with your opponents through strategy and tactics. my favourites are Imperial Steam and Caylus, but you can also start from Terraforming Mars for a more easier rules overhead :)

Overwatch has plenty of viable competitive heroes that don't require quick reflexes

Rocket League, f2p, one of its kind, high skill ceiling, reflex is not that important but does require practice and time commitment to play at higher level. I am 45yo and usually play around champ 1~2 in both 2s and 3s queue and only solo queue.

It's fun even at lower level unless you run into smurfs, but that will happen to every game.

There are no active cheat that gives cheater significant advantage. After last time dev ban bot users(first and only time since 2015) I have not run into any bot users online.(which means auto ban works really well). There are macro users but since it's macro they can't change what it did, and mostly only useful for kick offs.(which you can adapt and intentionally guide the ball where you want.) So it's easy to beat once a you play more. (Oh, and they ban those as well, so don't do it.)

Not sure if the X-COM PVP qualifies as competitive but it sure was a blast and it doesn't require any reflexes.

Are you me? I played sc2 not wc3 but feel the same way. I've been playing valorant which is CSGO style lots of holding corners and team tactics. Only really good if you have a good group to play with though. I also have a lichess account and the same desire for fog of war! Following this post for ideas :)

I recently noticed that 100% Orange Juice is actually getting a competitive scene, it seems.

It's a 4-player virtual board game where there's strategy involved in deck construction (one funny thing is that anyone can draw your cards so you have to choose carefully based on your choice of character and their special abilities), movement choices, understanding probabilities and other tactical decisions, and balancing risk/reward under uncertainty.

I used to be huge into the game but I haven't been following it for the past couple years or so.

Strategy games such as Pokemon or Yugioh might be well in your alley

Prismata is the best 1v1 turn-based competitive game. It even looks and feels somewhat like Starcraft.

It isn't very pooular, which I blame on bad tutorial and monetization decisions. It used to have just a series of missions for learning the game but in an attempt to make it palatable for a wider audience, the developers replaced it with a story and way too easy tutorial missions. The monetization is random loot boxes which doesn't fit well, as the game itself has no rng.

Unlike Starcraft, Prismata can be mastered simply by playing. (I went from bronze to gold in SC2 by not playing the game for years. It helped me focus on actually important things instead of getting my build order timings just right.)

Competitive Pokémon is something I’d definitely recommend. It’s similar to speed chess in that there’s a game timer but you have like 30 seconds per move to lock in. VGC is an incredibly deep and constantly evolving meta game. The NAIC tournament finished yesterday and is on YouTube if you want to see it being played at a top level with great commentary.

You can practice singles and doubles for free on pokemonshowdown.com. IRL contests held by The Pokémon Company are always doubles, played on Switch and will be played with Scarlet and Violet for the foreseeable future.