In the legacy File menu and in right-click context menus, 'New Window' related options are hidden when 'Always use private browsing mode' is ticked in about:preferences#privacy and instead only private window options are visible.

Additionally, the 'New private window' command in the Proton hamburger menu has 'Ctrl+Shift+P' as the shortcut, whereas in the legacy File menu it is 'Ctrl+N' (both shortcuts work however).

When in private browsing only mode, only the 'New private window' item should be available in the Proton hamburger menu, and the displayed shortcut should be 'Ctrl+N'

This issue breaks the Tor Browser
https://gitlab.torproject.org/tpo/applications/tor-browser/-/issues/40690
https://gitlab.torproject.org/tpo/applications/tor-browser/-/issues/40684
It should be given higher priority