The material IDs obtained through the following API are all computed using PBE / PBE+U (Optimize: MPRelaxSet, Static: MPScanRelaxSet), correct?
Not quite - MPRelaxSet and MPScanRelaxSet are both used for optimizations, whereas MPStaticSet and MPScanStaticSet are both used for statics. The difference is that MPRelaxSet and MPStaticSet are used for PBE GGA and PBE+U calculations, whereas MPScanRelaxSet and MPScanStaticSet are used for r2SCAN calculations.
Originally, MP did only PBE and PBE+U calculations. Around 2022, we switched to performing r2SCAN calculations preferentially. That’s why both input sets are used
If not, how can I identify which materials (currently on MP) are based on PBE / PBE+U, and which are based on r2SCAN?
Does the answer here help with this?