@Next-Stop, my guess is that it is not only dependent on the app, but also on the OS (and implementation of it, in case of an Android). My pixel 8 works perfectly with  a wireless keybord dongle on an OTG cable. You can start routes, enter destinations, press menu options etc.
@Corjan-Meijerink, I noticed only one detail: the scroll wheel does not work, therefore you cannot scroll through the folder structure when it does not fit on the screen. I am not sure if this is an OS thing or an app thing. Maybe the app does not catch the scroll action? Would be very nice to have a tablet with the app and a mouse to plan routes underway!