You’re right, turns out it does support MIDI sync from external MIDI, I didn’t notice this control before.
At the moment it’s not available to be enabled in the UI, we’ll fix that, in the mean time, you may switch the mode by hand:
sudo nano /var/modep/profile5.json
Edit transportSource line so it looks like this:
"transportSource": 1,
Save the file, restart MODEP:
sudo systemctl stop jack
sudo systemctl start modep-mod-ui
Then it will be listening to external BPM.