Games

thronefall is a fun little TD/RTS style game with a nice visual style and good rouglite-esque progression.

Crypt of the Necrodancer is great fun if they don't have it already.

I've been playing Jotunnslayer: Hordes of Hel recently on PC and despite being relatively action heavy it's 99% left hand (WASD + Q + space)

Most my time with Crypt of the Necrodancer was during a hand injury. It's of course a pretty intense game though, so it's not for everyone.

Papers please should be playable with one hand only and is great at burning time

One Finger Death Punch and One Finger Death Punch 2

What more is there to say? The reason why that works perfectly is already in the title of the game.

Caution: this game is addictive

A Short Hike might be a solid pick. It's super chill, no stress, and you can get away with playing it mostly with just the left stick and a button or two — easy to remap if needed. Spiritfarer could also work, though it might take a little tweaking depending on how much movement they can handle.

Dungeon crawl stone soup. Can be played with keyboard only.

https://youtu.be/vNvjdVJFW9A

Ben Heck made a couple of one handed controllers a few years ago. One of these controllers might open up more games than remapping buttons.

FTL ftw

https://www.gog.com/en/game/faster_than_light

Caves of Qud is keyboard only option (no mouse), mostly just need wasd. Definitely an atypical RPG but very fun all the same.

I went through the same thing a while back

I played a lot of turn based RPGs

https://store.steampowered.com/app/2008920/Lorelei_and_the_Laser_Eyes/

Brilliant puzzle game

Designed to be played on a controller with one hand so you can take notes with your other hand.

Such a cool stylish game. Highly recommended.

Not really helpful in terms of gifts as they are free to play mmo's and they use keyboard and mice but both have some script capabilities which allow for one to be able to play alternating between keyboard and mouse or not use mouse at all. Its the cryptic games champions online and star trek online. One thing you could do is play them yourself and learn the scripting and then gifting them useful scripts. with champions online turning the block to a toggle is the big script thing and with star trek online its making an emergency power to spacebar one (this is reference to a script where tapping space works through all the abilites put into a shorcut area that can be swapped out). really basic ones will dump everything into spacebar but more nuanced ones will have a key for low cooldown abilities and one for long cooldown offense and long cooldown defense. there really is no limit to the messing around.

One really handy thing with the Steam Deck is the ability to remap all of the buttons (as well as the two paddles on the back for each hand), so one could probably make a decent one-handed control setup for 99% of turn-based games. Even ones that require the use of the mouse, given the Deck's touchpads.

Vampire Survivors requires nothing except the stick/dpad outside of menus (and I'm pretty sure you can use the touchscreen for menus, too).

If your friend(s) are stuck using the dpad, it might not be suitable, but Crypt of the Necrodancer only requires four buttons or left, right, up, and down (and you can assign buttons for the button combos normally required to do things like use bombs). This assumes that they like rhythm games.

I remember that the dev of Legend of Grimrock added an option for movement with the mouse because a disabled gamer wanted to play. Maybe that second friend should check that and the 2nd game out.

Using a mouse with your non dominant hand is annoying…

Yeah, for PC they'll probably have to grit their teeth and power through the discomfort. An alternative is getting a hand in some old emulated games. Anything from the NES era can be mapped to 4 movements + 4 buttons (start, select, A, B), which on a keyboard could be WASD + Q, E, R and F. Dunno how to set something similar on a Deck.

deep rock survivor is a surprisingly fun and simple game that is designed for one handed play

So left hand only games.. driving games should work(enjoying NFS heat, atm), turn based games and isometric RPGs (plenty of those, depends on preferences... Balatro, slay the spire, XCOM, disco Elysium, etc... I could make a list if needed).

Telltale games like the wolf among us and stuff

Vampire survivors and all the similar games (halls of torment, brotato, soulstone survivors, etc)

If it's more permanent show them an Azeron Cyro at https://www.azeron.eu/ It's a mouse with a thumbstick, you can play almost any PC game with one hand. Comes in both right and left handed versions.

Pokemon Let's Go Pikachu/Eevee both support single hand mode.

Divinity: Original Sin 2 is basically just more BG3 (though with less production quality) so that should be right up your RPG-loving friend's alley. Turn based combat and click-to-move lets you play the whole thing with just your mouse I'm pretty sure.

Puyo Puyo Champions has a one-handed controller preset. D-pad or ABXY to move, shoulder buttons to rotate.

Only caveat is that if you want to play online, only the Switch version is actively populated, so I can't recommend the game on any other platform.

For the friend who enjoys BG3, you can play Pathfinder: Wrath of the Righteous pretty much entirely with the mouse. The base game is 90% off on steam right now too.

Pathfinder has a massive learning curve compared to DnD 5e though, but that just means you can get an extra 50 hours of entertainment out of the game before you start the story, just by figuring out all the options when creating your character lol

Edit: whoops, seems like the steam spring sale just ended. The game is still absolutely worth it at full price though