My M5Burner-Beta (2.0.0) offers 1.6.5-matrix as the newest. It does offer 1.4.5.1, which ends in 5.1.
Where did you get v1.6.5.1 from?

(If it's available, maybe it fixes my problem that the WiFi details aren't saved by the setup form!)

Does anyone know how https://github.com/m5stack/m5-docs/blob/master/docs/en/uiflow/advanced.md#p2p works - is it ESPnow-like, or are the messages routed via some m5 cloud service? I don't manage to find the source code of it to see for myself yet.

(I can't get it working, but I'm not sure if it's what I need anyway - I need the messages to work across different wifi networks via Internet.)

I'm not sure if P2P Read blocks or not.

PS: Where in UIFlow is simple 'serial print' ?