Hi,
Is it something in the pipeline near future that we maybe can choose/customize which option to be shown in the filter?
This is already offered. Go into the source type and choose Unique (predefined) and input the values you want to show up.
For date i can only see User Input source type
After testing I run into the same issues but only for the date field types. If you say the date "is on" rather than "is in" you can at least choose unique so they are selecting a date from that field.
Otherwise: if you just want it to say IS IN - 'this month' you can do that by choosing the specific timeline and selecting no user input