Calculated most used text in new column

DAX for Calculated Column

Outcome =
VAR CurrentCustomer = Table1[Customer ID]
VAR ProductCounts =
ADDCOLUMNS (
SUMMARIZE ( Table1, Table1[Customer ID], Table1[Product] ),
"ProdCount",
CALCULATE (
COUNTROWS ( Table1 ),
ALLEXCEPT ( Table1, Table1[Customer ID], Table1[Product] )
)
)
VAR TopProduct =
TOPN (
1,
FILTER ( ProductCounts, [Customer ID] = CurrentCustomer ),
[ProdCount],
DESC
)
RETURN
MAXX ( TopProduct, Table1[Product] )

You can create a calculated column like

Test = 
VAR ProductsAndCount = CALCULATETABLE(
    SUMMARIZECOLUMNS(
        'Table'[Product],
        "@num", COUNTROWS( 'Table' )
    ),
    ALLEXCEPT( 'Table', 'Table'[Customer ID] )
)
VAR Result = SELECTCOLUMNS(
    INDEX( 1, ProductsAndCount, ORDERBY( [@num], DESC ) ),
    "@prod", 'Table'[Product]
)
RETURN Result