By default that's Control+F4 (switches focus between all visible windows in all visible Spaces) and it "making sense on ISO keyboards" is irrelevant because (co

By default that's Control+F4 (switches focus between all visible windows in all visible Spaces) and it "making sense on ISO keyboards" is irrelevant because (contrary to your claim in a different comment that macOS is not customisable) you can in fact change every keyboard shortcut that shows up in System Preferences > Keyboard > Shortcuts as well as remap your modifier keys in System Preferences > Keyboard > Modifier Keys.