So to be clear Wayland + Pantheon resolves the issue but with a performance hit in games? X11 + Pantheon has the issue but with otherwise good performance in games?

Presumably all the system packages and software is up to date. If not then do a update.

Starting with the basics, what kind of mouse and keyboard do you have? If they are wireless, how are they connecting to your device? Note some manufacturers don’t provide drivers for Linux so it’s worth seeing if your brand and device is supported (E.g. Logitech and it’s wireless dongle; you need Solaar to get basic support and switching to Bluetooth may be best if available).

If they are wired, have you tried plugging the keyboard and mouse into different ports on your PC? If they’re on the same USB Bus that could be contributing to the problem. Although that really shouldn’t be an issue at all with modern devicss, it might be enough to get round whatever the issue is if one of your devices is conflicting.

Presumably if there is a power profile in Pantheon, and if so you’ve set it to performance, not something like balanced? This ensures that everything is running at full capacity. There are rare polling issues with wine and some USB devices, and one solution is ensuring the CPU is in performance rather balanced power settings to prevent a bottleneck.

If the issue is still persisting then I would next install a different Desktop Environment to see if the issue persists. This may help check if it’s an issue with Pantheon itself. Install a lightweight desktop environment such as XFCE. Try out XFCE in both X11 and Wayland, and see if the problem persists. If it doesn’t then submit a bug report to the Pantheon makers and consider switching to another DE (such as KDE or Gnome). If not then it at least helps seemingly exclude pantheon as the cause. It can be messy installing another DE and difficult to remove cleanly so one method is create a backup of your system using Timeshift, and then restore it after trying XFCE to bring your system back to its original state.

If the issue persists you could also try switching to an older version of the Nvidia drivers or the open Noevaeu drivers. If it resolves it that helps narrow the problem although if it doesn’t resolve it you still can’t entirely exclude the graphics drivers as the cause.

I think assuming all the basics make no difference, the most telling test will be if switching from Pantheon to another DE helps - in X11 and Wayland. Pantheon is relatively niche and DEs are also important factors in themselves when it comes to performance and also bugs. If it persists beyond a DE test, then I’d be most suspicious it’s a driver issue either with the devices themselves or the graphics drivers.

Not much more I can think of beyond that at the moment sorry.