Retrieving the current page filters

I don't think that this will be possible because of the way filters work. Even if you specify the condition as a boolean, filters are always tables of values which already exist in the data. For example, if you specify 'Table'[Column] < 5 as a condition, that might be translated into a list like { 0, 1, 2, 3, 4 }. But if you don't have any entries where the value is 3 then the list would be { 0, 1, 2, 4 }.

Given that, if you try to use as a filter a value which doesn't exist in your data then Power BI will basically just throw that value away.

Having said that, you might be able to detect the fact that a missing value was passed in, even if you can't detect what the value was. You could create a measure like

Missing value used as filter =
IF (
    ISFILTERED ( 'Table'[Column] ) && ISEMPTY ( FILTERS ( 'Table'[Column] ) ),
    1
)

This checks that there is a filter applied to the column, but the values or condition applied don't match any of the existing data.