Lets imagine you want cases with at least one activity in the last 12 months....

FILTER ACTIVITY_TABLE()."EVENTTIME" > ADD_MONTHS(TODAY(),-12)

Thanks again @Guillermo Gost for your help. I had been looking at the ADD_DAYS, ADD_MONTHS but wasn't sure it was the correct approach.

Was hoping to avoid using TODAY() as this is essentially a moving target.

Do you want always a fixed date? Or maybe a moving target but like init or end of month?

Fixed date will be something like this instead of the TODAY()

TO_DATE('30-4-2023', FORMAT ('%d-%m-%Y')

BTW if the date string comes from a table and you get other data formats (like the name of the month instead of the number, or a 2 digit for the year) Celonis is a bit limited compared to datetime library... so you will need to apply some CASE WHEN to convert (like CASE WHEN "April" THEN 04...)