Going back to Kodi’s menu with the gamepad while playing a game?

I’m using LibreELEC nightly with nothing but a bluetooth gamepad to control my Kodi box

In Retroarch/Lakka, while I’m playing I can press a particular combination of buttons to go back to the Retroarch interface.
Like for example Start+Select or L3+R3.

How can I switch from playing a game in Retroplayer back to the Kodi controls/interface while using my gamepad?
I couldn’t find an option, and it doesn’t look like changing joystick.xml would allow me to define a button combination for it.

Other than this detail, the experience is already quite nice in Kodi 18 nightlies.
I miss a “Recently played” list in the Games section of Estuary but I understand that this is still very early for Kodi 18 and only recently was Retroplayer merged.