You can use this measure to count
Count Measure = SUMX(FILTER(SUMMARIZE('Table','Table'[Serial numer],"Count",COUNT('Table'[Name])),[Count]>1),[Count])
If you want to display the names in the report, you can use another measure as a filter. Add Name column to a table visual in the report, then add below measure to filter pane as a visual-level filter on this table visual. Set it to show items when value is 1.
Filter Flag =
var vSNs = SELECTCOLUMNS(FILTER(SUMMARIZE(ALL('Table'),'Table'[Serial numer],"Count",COUNT('Table'[Name])),[Count]>1),"SN",[Serial numer])
IF(SELECTEDVALUE('Table'[Serial numer]) IN vSNs, 1, 0)
Community Support Team _ Jing
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