Management games, strategy games, point-and-click games and isometric RPGs can all be played one-handed. Some might need spacebar (or whatever the pause button is) to a mouse thumb button for maximum comfort but that should be fine. Do any of these genres sound interesting?

EDIT: Card games should work great too, there is a vast ocean or deckbuilders out there!

Have you considered using the pedals of a steering wheel and configuring that to take the work from your left hand to your feet?

Frostpunk is the first mouse game I've played in a decade. it was really nice. it's a citysim but you have to prolong the life of a civilization through the heat death of the universe. Since every end state is freezing to death it makes you consider living in an interesting way.

also it made me cry which is a really weird emotional beat for a citysim. who does that?

Point-and-click adventure games can be played with just the mouse. Full Throttle is about bikers.

Something I haven't heard recommended yet: One Finger Death Punch 1 & 2. It is completely mouse based, pretty addicting, and satisfies the itch for interactive stick figure fighting like the old Flash videos used to do.

Keyboard and mouse setup with old school DnD. The games that move your entire party with a single mouse click on the map.

Baldurs Gate 1 & 2,

Planescape Torment,

Neverwinter Nights campaigns 1-3,

Neverwinter Nights 2, 1 & 2. MotB is artfully made. And you get to heroic and levels.

Iirc Dragon Age Origins has a similar setup, BioWare breaks from the format in later editions.

There’s always 4x. Endless Legend is neat. Stellaris. Civ for classsic content.

Vampire Hunters

Maybe racing management game ? I found Motorsport Manager on Steam, i never played it but it looks like it's playable with only a mouse, and it has excellent reviews.

Holy fuck, you blended your hand? Is it okay? Is it intact?

Trackmania would be my recommendation, you can do almost everything using just the arrow keys and mouse for menu navigation. 

Slay the Spire 2, you just need the mouse. And yes you can race, you can speedrun dying lol.

Have you considered turn based RPGs?

Great time to try the Monkey Island games

• Play Rimworld

• Get addicted

• ... Profit?

Check out brotato. It's a cheap game but it's got an addictive gameplay loop, all you have to do is move a character around. I've put over 100 hours into it, and each session is pretty short.

Perhaps switch to a keyboard for the time being?

I severely broke 3 fingers in my left hand half a year ago and was able to play Elder Scrolls games and Tux Kart surprisingly soon after the accident.

Sufficient to be able to just move the flat hand left and right a bit and get the fingertips a few mm down to press a key.

Being able to use a controller again took more than 2 months and wasn't even fun then (did it mostly for the therapeutic training effect).

Old school runescape can largely be played one handed.

Also feel like I should mention Euro Truck Simulator 2 and American Truck Simulator.
Not exactly racing themed unless you play it very badly but I promise you it is way more fun than it has any right to be.

I'm currently playing Cocoon, it's a fun little indie gem with only an analog stick and a single button to control it, and an accessibility mode in the controls settings that makes both sticks and all buttons work; so you can play with just a stick and trigger -- one hand.

How about getting a joystick and trying some flight sim? It can definitely be done with one hand!

Worldbox, Sky: Chilren of Light might be able to be played this way if it can be rebound, Caves of Qud can be albiet slowly (but its not a fast game anyway), Solium Infernum can be played one-handed.

If you have or get one of those thungs from Razer or something equivalent where it has the key group, a joystick thing, and some more inputs all on one hand you might be able to configure a lot of games to be essentially one handed

Visual novels like Doki Doki Literature Club! and Z.A.T.O. // I Love the World and Everything In It come to mind. Both are free and pretty good.

Not racing but "Autochess" is a pretty fun genre which can be played with one hand. Games like Mechabellum, Teamfight Tactics, DOTA Autochess etc.

As you've already got a wheel and pedals, how about something like Euro/Amer Truck Simulator? It's slower paced than racing, so wouldn't require as much dexterity and button bindings/shifting can be configured to inputs you already have.

This isn't racing but I was thinking about it this weekend:

Cobalt Core is a fun roguelike deckbuilder about escaping a time loop in a spaceship that I feel doesn't get enough love. Definitely one of my favorites.

The characters are cute but not painfully so. They have unique personalities and every time you "win," you unlock bits of the story of how everyone got there.

Telltale Games would work well I think, Tales from the Borderlands is my recommendation from those.

You don't need to have played Borderlands games (atleast I didn't) and it's a funny engaging game, I don't know how good you are at mashing buttons right now though since the game does have a couple of fail states over those

Lol my dirty mind went to eroge VN but any visual novel would be good, or point and click adventure games, 4X games like Civ, or turn based RPGs come to mind.

Been there before. The Wii has tons of one handed games. You can also do stuff like Pokemon games and other slow rpg's.

If you have a keyboard, anything that supports vi keys is one handed.

rhythm doctor?