How to calculate unique count based on multiple column values

You might try adding a FILTER function to your measure. The concept is the same, but the syntax should allow multiple columns in the condition.

Test 2 =
CALCULATE (
    DISTINCTCOUNT ( sj_strata_encounter_hb[FINNBR] ),
    FILTER (
        sj_strata_encounter_hb,
        OR (
            sj_strata_encounter_hb[MS DRG CODE] IN { "10", "266", "621" },
            sj_strata_encounter_hb[ADMIT ICD10 DX CODE] IN { "S48.23", "C24", "P12" }
        )
    )
)