2001 Audi tt has been driving find until one morning while at a drive thru shifted what I though was first gear car will not move seems to be stuck in first but car is actually in neutral. Let off clutch pedal no jerk or anything car rolls. Cannot move gear box . Pooped the hood removed shift linkage from transmission shift boot shifts freely so that rules out and linkage problem . While linkage undone tried to manual move shift adjuster nothing it's locked into neutral. What could this be. I wanna rule out its nothing to do with the locking pin/ selector/ nothing that I can fix externally before I decide to pull transmission out.

Any advise or help will be greatly appreciated

Even with engine off still cannot shift into gear so that should rule out clutch issue.