I’ve never played Halo Infinite or used Mint, so I’m going to have to be a bit hands-off. I’ve no idea if there is a trivial fix, or whether you’re using Wayland or whether you’re using an Nvidia/AMD GPU, but I can try give some suggestions.

The mouse movement also feels off like I have mouse acceleration on or input lag.

Well, it could be using the windowing environment’s mouse acceleration. Is there an option in Halo’s video settings for something like “fullscreen” or “borderless fullscreen”/“windowed”/“borderless windowed”? If it’s any of the latter, my guess is that it’s most-likely using the windowing environment’s acceleration.

A reasonable test might be flipping off your desktop environment’s mouse acceleration, running the game, seeing if the issue goes away. I don’t think that there’s any non-desktop mouse acceleration layer that could be causing it.

I’m not familiar with the issue, but I also see some discussion online about Proton-GE – the GloriousEggroll build, not Valve’s – intaking patches for raw input.

https://www.reddit.com/r/linux_gaming/comments/1b9sga3/wayland_mouse_sensitivity_inconsistency_in_game/

But I don’t know whether that’s relevant to Wayland or not (or whether you’re using Wayland). Probably wouldn’t hurt to give Proton-GE a shot, though, rather than Proton Experimental, if you’re otherwise unable to resolve it.

When I run the game on windows I get 144 fps almost constantly on Linux I get 70-80.

The first thing I’d do is glance at the ProtonDB page, see if anyone has run into performance problems and has a fix. That’s a good first stop for “something under Proton isn’t working the way I want”.

https://www.protondb.com/app/1240440/

If that doesn’t help…

I’m guessing that you have a 144Hz-capable monitor and that it’s running at 144Hz in the game in Linux, just to rule out anything silly like the monitor refresh rate being low and running with vsync?

If so, I suppose that the next thing I’d look at is whether your CPU or GPU is the bottleneck, as it’s most-likely one or the other.

There are various HUDs to look at that. I don’t know what’s popular these days.

Looking at the Halo Infinite ProtonDB page, I see people talking about using mangohud there, so I imagine that it’d probably work.

The GitHub page says that it can show both CPU and GPU load in-game.

https://github.com/flightlessmango/MangoHud

If that doesn’t work for you, if you have an AMD card, there’s a utility called “radeontop” that will let you see your GPU’s load. It runs in a console. I don’t know what desktop environment you have set up in Mint or what Mint even uses by default, but if you know how to flip away from the game to another workspace there, you can take a look at what it shows. It looks like Nvidia’s equivalent is “nvidia-smi”. I’ve used those before when monitoring GPU load. The top command will show you how many of your CPU cores are active.