Using a German keyboard on a mac, I can type a " \ " (backslash) using ⌥+⇧+7 (alt+shift+7). So adding the ⌘ (cmd) in Figma (⌘+⌥+⇧+7), let’s me show/hide UI. But since this 4-key shortcut, is a real pain, I’m very thankful to the hints I got here: there seem to be several ways to show/hide UI on a German (mac) keyboard:
⌘+.
⌘+#
⌘+⌥+⇧+7
and the right-click on background is also very useful.