The only workaround I’ve found is to connect an Xbox controller, which will override the keyboard as a means to control the UI.
You will see Xbox controller-specific button short cuts. Pressing ‘B’ will allow you to Return to Briefing.
An alternative is to base your entire keyboard mapping profile on the 2024 Transversal rather than 2020 Transversal.
Either way, it is ludicrous that the ability to control the interface via keyboard is non-existent when deviating from the 2024 Transversal keyboard profile.