Hello @michael! Sorry, my bad, for some reason, I was sure that in Baserow filtering works on the formula field type but it turned out that not 
What you can do is use the FILTER function. It “filters” a range of data based on specified criteria. Let me show you an example of how it works:
Let’s say we want to filter and show only fields that contain the letter ‘a’ in the column ‘Lookup’, and by using this formula we can achieve the needed results:
filter(field('Lookup'), contains(field('Lookup'), 'a'))
Unfortunately, this solution is more complex but hopefully helps for now. I can also confirm that we plan to add the possibility to filter on the Lookup and Formula field types in the future.