Bottom and sides look good, so it’s just a top-layer problem.

To me that rules out inconsistent extrudion or a wrong steps-per-mm setting (which would cause under- or overextrusion), since all these things would be visible on the sides too.

The two first things I would check would be:

• Is infill off? You should have at least 5% infill, better 10-15%, otherwise you’ll print in thin air causing issues just like that, with the edges looking ok and the closer you get to the middle getting worse.
• Is the fan on? Especially on PLA and fast print speeds the fan should be constantly running at 100%.

Pressure advance would be the next one. To check whether that’s the issue, turn the print speed way down to maybe 50mm/s. At that speed pressure advance hardly matters, so the issue should disappear. That test only works if you ruled out infill and bad part cooling as culprits, since slowing down the print will also help for these two issues. Tuning pressure advance is not trivial though.