The most common problem we see with dryer vents is with roof terminations of the dryer vent pipe where the home has been re-roofed.
The correct vent is the first photo. The screen must be removed for use with a clothes dryer or it becomes blocked with lint and poses a fire hazard.
The second photo is an off ridge attic vent which is not designed or intended for use as a dryer vent.
These are regularly installed by lazy roofers. Their use poses numerous issues for the home owner.
#1: It will become blocked
#2 it will cause the dryer to vent moisture into the attic possibly damaging the roof decking and creating a lint fire hazard in the attic.
Blocked vents stop the air flow extending the drying time required
which increases the cost for drying each load in the dryer