What regular maintenance do you do (or pay for) on your house HVAC system?

Im not originally from Houston, or a place where HVACs are used. So this is all brand new to me.

Ive lived here a few years, and never done anything to my AC (other than replace the filters and pour some bleach down the drain pipe) – other than the one time it felt like it wasn't blowing cool air and a tech came out and said my coolant was low and topped it off.

Kinda confused about that as I believe the coolant system is a closed loop system so it should never need to be topped off? or does coolant just go bad and need to be replaced?

Anyway, that was a few years ago and my AC system isn't blowing that cold anymore.. so I think I need to be 'topped off' again.

I was speaking to my buddy who says he pays an AC guy once a year to come out and service his AC. He didn't really know what he did, but he said that I should be doing this yearly.

What kind of service would be required? what does a tech do on a yearly service?

The only stuff I've had to do over the years which was out of the ordinary repairs was to replace the capacitor battery on the outside unit when the fan stopped spinning, and also one time the PVC drainage pipe in the attic got blocked (on the small section before the fill port when I pour the bleach) so I replaced 1ft of pipe where the blockage was.

Is there anything else I should be routinely doing?

Are you guys paying AC guys $$$$ to come out once a year and take a look at your unit?

Looking for advice as I thought I had my bases covered, but maybe I don't.