Car having trouble reversing?

Two possibilities. Either the transmission is failing, or it is leaking and the fluid level is low. Check the fluid level, fill as necessary, and see if the problem goes away. If it does, try to find the leak and have it fixed. If it isn't low on fluid, your transmission may need to be overhauled.

Ck. the fluid with it being hot and idling in park, if its a automatic.

possible transmission

Sounds like the transmission is starting to slip. Start saving for a rebuilt transmission or sell the car now and find a different ride.

If a manual trans, could be the clutch is nearly worn out and slipping seriously. Soon it won't grip at all and you'll need a tow truck to get it to a shop. Try this; put the transmission in the highest gear and try to drive off. If that doesn't stall the engine right away, the clutch is on its last legs. If automatic, have an OBD2 code check done free at a car part store. Write the code down exactly, then study its definition: https://www.obd-codes.com/trouble_codes/

Check your back brakes as well as the trans. fluid.

Low transmission fluid level

Have you checked the transmission fluid level?

CVT on the car? Check the fluid and check for codes with a scan tool.