If your car has an interlock cable for the shift lever then the interlock cable could be stuck or binding up somehow.
You might need a new interlock cable installed because they can wear out and become stuck or break after so many years of shifting the cars transmission into the different gears.
Some vehicles also have a shift linkage instead of the cable so the linkage could be binding up underneath the vehicle as well.
I have an old truck that has the linkage and if you drop it down in the last gear then you can't shit it back up until you shut the truck off and crawl underneath the truck and move the shift lever by hand.
So sometimes it can be caused by a stuck or binding shift linkage or a shift lever cable that operates the vehicles shifter on the transmission.
I would take it to a mechanic and have them check it out or crawl under the car or look where the transmission is if it's under the hood and look at the linkage while someone moves it back and forth.
Something could be binding it up at the transmission or the cable could be worn out and is about to break.