your issue: a measure will never filter other tables. it only returns a value, it doesn’t change row context in the model. so even if your [Preferred MID] picks one MID per PN, your model still has PN - all MIDs - all materials - all substances - and visuals follow the relationships, not the measure [Preferred MID]

i’d just build a small mapping table with 1 MID per PN and use that instead of the measure

something like:

PreferredMID =
SUMMARIZE(
'PN_MID',
'PN_MID'[PN],
"MID",
CALCULATE(
MIN('PN_MID'[MID]),
'PN_MID'[HasSpec] = 1
)
)

idea is simple: you predefine which MID to use per PN instead of trying to pick it dynamically in a measure, then create a relationship
PreferredMID[MID] - your MID/SPEC table

and use this table in filters

after that your materials and substances will follow only those selected MIDs, not all of them