Transmission not engaging gears

My car had issues that began two weeks ago; revving high 4,000's rpm before changing up gears.
About a week in, I lost reverse gear, would rev like it was in neutral, like it just wasn’t engaging. I found the issue was corrected after turning the car off and returning to it the following day. Then 2 days later I stopped briefly and placed into park to chat to a neighbor then when returning it to drive, it suddenly refused to engage any forward gears. It wasn’t until I completely turned off the car and allowed a few minutes, restarted and placed into park would it go again, further inquires, fluid checks, another day of driving, it would only go up 2 gears before slipping into wot felt like neutral or a limp mode?
Rapidly it had gone from perfect no-clunking, no slipping or rough changing to not being able to engage any gears at all. Checked levels numerous times and ways, fluid like new with no burnt smell. Have read A lot of varied answers to similar questions, this car has only 90,000 km and previous owner 92 owned since new. Surely this can’t need a new gearbox? And since the issue seemed to somehow disappear or reset after turning off ignition for 20 seconds wouldn’t this suggest more electrical issue than a mechanical one? And Which electrical part would cause this and then reset? TPS, TCM solenoids, selector cables.
Single mum who supposed to be driving it for work tomorrow, so long investigations and costly lengthy repairs on a 20 year old car isn’t something I can afford or want, but with such low kms and condition I honestly thought I wouldn’t have issues with this car for quite some time.