Return line is “farting” with air and bubbles

You could be having a suction side air leak. First thing to check is the oring seal where your pump top locks on. Remove it and check for any cuts or nicks, if not, lube it real well and tighten securely on to the pump.
Is this a new problem with the pump taking 30 secs to prime and air from the returns? Have you done any recent changes in the valves or other plumbing activities?
Post a picture of the whole equipment pad and also a close of the pipes going to the suction side of the pump.

How do you chlorinate your pool water? Do you use pucks, liquid chlorine or a saltwater system?

Take a garden hose without any sprayer attached and let it run over that pump lid with the pump running and see if the bubbles stop. If not, run the hose on any exposed piping and valves and see if the bubbles stop. Keep this up and see if you can find where the air leak is.

Had a family member with the same issue and the hose method found a leak at one of his valves.

Do the "farting" bubbles have a bad smell? If so, you may have another issue altogether

Check the weir (skimmer) door, make sure it's not stuck in the closed position. From the photo you posted it looks like your water level is okay, but double check. The water level should be halfway up the skimmer mouth. Take a look inside the skimmer and see what's going on while the pump loses prime.