This vehicle appears to have an automatic transmission fitted.
So if it has been juddering and now barely moving - this would suggest that there has been considerable fluid loss from the transmission unit.
I would advise that the fluid level needs to be checked, by an experienced mechanic or audi dealer / specialist.
If the fluid is too low - then the internal transmission oil pump is unable to pump pressure around the transmission to enable it to operate.
This will also cause the gear friction clutches to slip. If they slip - they will over heat.
Unlike a conventional Manual transmission - the clutches should never slip - they should only be on or off during the transmission operation.
I hope this helps you understand and assist with resolving your concern.