This little piece of metal (biro tip for scale) below snaps in a particular make/model of UPVC door multipoint. If it breaks the door is jammed shut. The same part had broken off in 6 other doors at a single property we attended recently. That rendered all the doors jammed shut.
The doors were carelessly installed / had moved out of alignment. Correctly aligning the doors when they became difficult to lock would have prevented this failure. Instead the problem was ignored until one by one, the mechanisms broke and the doors couldn’t be opened. That 1.5mm x 2mm piece of nasty diecast metal will snap off if undue force is required to lock the door.
The particular component shown below from another particular UPVC door make/model is responsible for around 80% of door failures in new/recent builds that we get called to. We can see 2 or 3 of this broken part in a single day. It’s not unusual for a badly fitted door to jam shut the day the customer has moved in, or the builders haven’t even handed it it over yet.
Squirting WD40 in the lock, or filing parts off the frame might make your door work better temporarily. Unless you correct the fault it is just delaying the inevitable.