The only screwed on connection on toilet drain line is the floor flange..all other fittings are glued to pipe.
If it is the toilet floor flange leaking then you have to remove toilet, remove screws thru floor flange into floor before it can be removed/repaired.
Floor flange threaded portion may be cracked.
I would remove flange and replace. A small crack can be repaired with some epoxy but if it doesn't work or cracks again in future it will just be harder to remove/replace.
The toilet floor flange seal is a foam gasket that rarely leaks water......they are more for sealing out odors as the water drops straight down vs flowing down.
If leak is on a pipe fitting (coupling) it can also be repaired using epoxy.
If repair doesn't work then pipe will have to be cut into and a new coupling glued on plus longer pipe.