I rent and don't go under my deck often. Tonight I noticed one joist is black and falling apart. There are sections where you can see through the joist completely. The floorboards are trex and bow up where the joist is. Is this deck still safe to use and should I submit a maintenance request?
Stay off. Call your landlord.
That is firewood, no longer a joist.
Deck wont fall with a single joist failing, but do take care of it.