Shifter linkage to transmission: bushing and clip mount?

check the shift cables that runs from gear lever to transmission

Sounds like linkage from shift lever to transmission or the bushings on the linkage points. A "sloppy" shift lever with similar bushing problems may be the problem.

It appears this is a 5 speed manual transmission. There may be shift linkage problems between the shift lever and transmission. also bushings. I strongly recommend a repair manual specificly for this transmission. possibly filespeep.com or manualslib.com
How is the clutch and throwout bearing?

Check the linkage under the stick console. May be lose or broken.

Start with the firs post and have those cables and linkage assembly looked at if those are good then what you have is a loose bolt on the transmission that bolt is responsible to keep the gear in place when loose the transmission will do what you described as well nothing more nothing less.

There are bushings in the linkage for the shifter under the car at the shifter and at the trans. Those wear out or the retaining pin clip may have come off and pin got loose.

Does that transmission have external shift linkage? Sounds like a linkage broke or the neutral gate is way off.

It could be a couple of things. Could be a simple as shifter linkage bushing linkage, to a bent shifter linkage rod. Another "rare" possibility is a motor mount. If mount breaks, engine postion/angle changes and puts stress on everything from engine rearward.

if u have the old one have machine shop repair and or fabricate a new one go online search for parts alot of salvage yards post their inventory and ship parts may get lucky but good luck

The linkage is basically a large rod that runs from the shifter to the trans with a bolt at each end like a universal pivot. They ususally get sloppy because the bushings wear out. But that would not make it where it would be stuck in gear. If you cant get it out of gear the trans may need to come apart.