Is this mold or what!?!?

Anybody have any clue what this is? It started small and is slowly growing. Only on one plant currently but not sure if I need to fix this or what. Kinda looks like mold but it’s only on one plant and humidity stays between 40-50 and 60 on a bad day.

looks like stem rot to me, be prepared for that whole branch to come off, maybe even get to the main stem if it spreads

@go go kid Anyway to prevent from spreading? Should I clip branch and scrape off the rest?