can you try
dt_fb.Select ("[Period From] < #01-05-2022#').CopyToDataTable()
we used
[ ]
to surround the col name as it has space#
for a date compare
https://www.csharp-examples.net/dataview-rowfilter/
when an empty result can occur handle it as described here:
When it is not working then share with us the datatable content by using the immediate panel