Few minutes after buying a 2007 manual, pulled off the road, needed to back up, but the car croaked when trying to engage in reverse and it didn't engage.
Things I know:
1. If I first engage 1st gear, I can shift into reverse with no problems at all.
2. If previously the car was engaged into any gear, including reverse, I can't shift into reverse.
3. If I slowly try to shift in reverse, the stick will stay in reverse, but if I slowly lift the foot on the clutch, the gearbox jumps itself on neutral, unless I hold the stick with my hand in reverse.
Something similar happened to my dad's 2008, sometimes, to engage 1st gear I needed to shift into 2nd. His problem disappeared after changing the fluids.
The car is scheduled for service, but I'd like some opinions.

It's actually pretty common for the gears to fail to select without a little help, even on a brand new car.
This happens because the gear cluster doesn't always stop rotating in the correct place for the gear you want, especially in reverse.
Sometimes just selecting another gear is enough to rotate the gear cluster to a suitable position, sometimes you need to lift the clutch in neutral, then try again, which also spins the gears with the hope you can get the gear you want.
Also on an all synchro gearbox like the Freelander box, you can't select reverse if you are still moving forward, which again is completely normal. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Maybe, but these 3 I've described above happen always, not just sometimes.
And no, I didn't try to reverse while moving at all.
Also, one thing I forgot to mention is that the clutch seems a bit rough, has a short clutch stroke and as much as I try, I can't go forward from a standstill without a bit of shock when lifting the clutch

Sounds like the clutch is almost out. The clutch should engage smoothly and progressively. Clutch snatching or reduced progression is a good sign that the plate is wearing thin. This can also cause the friction material to distort slightly, which keeps it dragging enough to spin the gears in the box, making it difficult to get gears to mesh. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.