Most likely issue is the pressure is getting low

ALL automatics run on Pressure, since they were first invented, electronics doesn't change that.
Forward motion needs 125+ PSI at the right passages
Reverse needs 160+ PSI at the right passages

This higher required pressure is why Reverse is slow to engage or lost first, when there are pressure problems

Yes, you can add trans-fix or other similar additives, these swell seals and gaskets to help keep pressure up.
Its a stop-gap thing, not a "fix"

If you pull the pan check it for metal flakes, this would indicate a mechanical issue so rebuild needed for sure.
If pan is fairly clean then you may be able to just replaced Valve Body and seals to get pressure back up and flowing in the correct passages

Running an automatic with lower pressure causes higher wear on clutches and bands(brakes), so...........best to get the pressure back up

There are ports on the side of automatics were pressure can be tested, need a high pressure gauge, 300+ psi