Comment by troad

You can try to remap KDE keybindings but it won't affect Gnome applications, games, etc.

Personally, I found the most reliable thing to be a keyboard-level swap of Ctrl and the Cmd key. That way, whenever you're asked for Ctrl, which is all the time, you can always safely hit Cmd with no need for extra configuration. You can then remap various things in KDE Shortcuts to be more Mac like, like Cmd+Q, Cmd+Tab, Cmd+`, etc. (The only thing lacking is the Ctrl v. Cmd separation in a terminal, so I manually remapped all the Ctrl sequences in my terminal emulator to Win sequences, which matches my hardware Ctrl key. So, like on a Mac, Cmd+C works to copy, Ctrl+C is the escape code.)

This works for a Mac keyboard. For a Windows keyboard, you'd have to shuffle Alt -> Ctrl, Win -> Alt, and Ctrl -> Win. There are settings for this in xkb. (KDE surfaces these in its Keyboard settings panel.)

Keyboard layouts/shortcuts are a huge pain point with Linux. xkb is geriatric, and acts as such. Compose keys are flaky and inconsistent across applications. Virtually all Linux software is going to default to some idiosyncratic take on Windows shortcuts, often without much by way of customisability. (And those Windows shortcuts weren't very good to begin with.)