Try plugging a mic (ideally one that does not need phantom power) directly into the desk – first in a working channel to prove it works, then into channel 6.
Can you hear anything in headphones when you solo it/ see anything in meters?
If not double check the source is local, not dSnake
If you get something then: (You may have done all of this)
Check:
Mute & Mute groups
DCA Groups (if assigned to any, are they up & un-muted)
Is the channel assigned to L+R (or whichever output you want)?
If you get nothing with PFL though, maybe try plugging something into the line input of channel 6 (again having proved it works on another channel first)
Still no joy then it’s save settings if you need them and do a simple desk reset from the scenes screen.
If that still gives no joy you could look at a full reset……