Linux

Wayland has much better multi touch support on many laptop touchpads. I would definitely recommend trying it out on your Thinkpad.

You're not running Nvidia so your desktop would probably work fine on Wayland as well. Wayland has improved privacy protections so it's possible screen recorders that haven't been updated in a few years break; most standard KDE tooling should work without issue, though. Wayland is missing some features X11 already has, and things like colour profiles are stoll in development; if your display needs a specific color profile to look right, you may want to stick to X11.

Performance should be very similar. I haven't noticed any difference. The scrolling and gestures are a lot smoother but that's not necessarily a performance issue, that's just X11 not being able to cope with modern touchpads. Wayland itself isn't a performance problem, in fact the Steam Deck game UI runs a custom Wayland implementation and that's basically a games console.

You can just install Wayland support on KDE (if it's not installed already) and select it from the desktop environment drop down on the login screen. If it doesn't work or isn't to your liking, you can always log out and log back into an X11 session.

As for i3, you'll probably need an alternative such as Sway as i3 is very much X11 only. There are a few very fancy i3-like environments for Wayland but it's up to you which one you want to give a go.

I've mostly switched to Wayland on my laptop, but that does cause some Nvidia related problems every now and then. The integrated Intel GPU works great, but as usual Nvidia makes life harder for everyone. My desktop has an Nvidia card so enabling Wayland causes video decoding issues and weird performance issues.