Flushing is fine for what it does. Your filter is evidently installed backwards, as the flow arrows show correct flow from left to right, but you say flow is right to left. However, it looks like the pressure tank is to the left, so...? I use one of these "spin-down filters" with 200 mesh stainless steel screen myself, but it's installed in the right direction.
If you wish to clean it more, or (if you are having grit get through it) replace with a finer filter screen, shut off the water on both sides and unscrew the whole clear canister, after releasing pressure with the bottom valve. Someone has complicated that by attaching electrical conduit as a hose (seriously janky) to the bottom valve, which you'll have to remove to remove the clear canister. If it's the same maker as mine, the stainless screens only go to 200 mesh, but polyester screens are available up to 1000 mesh. You can add a different type of filter after this if you have material getting through that's too fine even for that.
Due to physics, it will also work a lot better if the flow is the correct direction, as it's supposed to "throw" heavier stuff out of the water stream by centrifugal action, when flowing the right way. And the flush valve is probably not flushing the collected junk on the screen very well, as the collected junk that hasn't passed through the screen will be on the wrong side of the screen, if it is indeed backwards, as it appears to be.
If the place it is is not in full darkness except when you are working on the pump, it's advisable to put an opaque cover over the canister to prevent algae growth. How often to flush it depends on how fast it fills with crud.
There's no schedule that isn't directly affected by "what does your well cough up to clog it with" and that's going to be unique to your well. For some wells, it also changes by season of the year. You can get a related but different version with a larger area for crud to collect between flushings, below the filter section.