Sorry for this newbe question, maybe also in some extent OT.
Is it any (free) MQTT client for Android that can interface with flespi MQTT broker?
You can use mqtt-board https://flespi.com/tools/mqtt-board
Just open https://mqttboard.flespi.io/ in browser 😉
MQTT TILES on mobile is good ,
if you are looking for native android app with push notifications etc ,
and MQTT dash app works with Flespi MQTT broker