Looking at your video, it does appear that the cut out in your door is too narrow to allow the lock to pass through. Check to see if there is a trim piece that comes off the door to access the lock. Another idea would be to remove the door from the track to see if the lock can slide out from either the top or bottom of the patio door handle stile
I have the same issue with my patio door. I am able to pull the trim from the top of the patio door frame down to below the mortise lock. Then I will be able to do the replacement from that point. See attached photos.
For reference my patio door is a 2006 Milgard sliding glass door. The lock snib (the part of the handle that you move to engage the lock) is "floppy" which presents the risk of locking us out if the patio door is shut while we are outside. Since I will not get the new mortise lock for a week or so, I simply turned the old mortise lock over so the lock snib functions the opposite direction (snib moves up into the lock position and down into the unlock position). I will be installing an additional lock at the bottom as well.
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