Loop through table column with spill formula

MichielS340 

You're receiving the #CALC! error because BYROW is designed to return a scalar for each row - 7 rows, 7 scalars.

One approach is to use thunks. For example, 

=LET(
    i, SEQUENCE(ROWS(Table2)),
    thunk, LAMBDA(x, LAMBDA(x)),
    thunks, BYROW(
        Table2[Begin],
        LAMBDA(x,
            LET(
                StartDag, x,
                EindDag, OFFSET(x, , 1),
                AantalUur, OFFSET(x, , 2),
                NettoWerkdagen, NETWORKDAYS(StartDag, EindDag),
                LijstWerkdagen, WORKDAY(StartDag - 1, SEQUENCE(NettoWerkdagen)),
                UurPerDag, AantalUur / NettoWerkdagen,
                thunk(
                    HSTACK(
                        LijstWerkdagen,
                        EXPAND(UurPerDag, NettoWerkdagen, , UurPerDag)
                    )
                )
            )
        )
    ),
    DROP(REDUCE("", i, LAMBDA(acc, v, VSTACK(acc, INDEX(thunks, v, 1)()))), 1)
)

There are several discussions in this forum that cover thunks thoroughly.  This site is a good primer for getting started:

What is a thunk in an Excel lambda function? - FLEX YOUR DATA