https://puu.sh/GKZFs/cd84b36cfc.png
https://puu.sh/GKZFW/ffd11e8af4.png

doesn't matter what i put in activityname:find("xxx") - it's errors. how to use it?

Apparently this is no longer possible since BFA prepatch :

https://github.com/0xbs/premade-groups-filter/wiki/FAQ#how-can-i-exclude-groups-with-wts-or-boost-in-the-name

Searching by activityname should still work (name and comment do not). The find function returns nil if no result was found, so try to use e.g. activityname:find("dungeon")~=nil for searching for the word "dungeon". Note that you have to keep it all lower case and that the acitivity name is just the gray text underneath the title (yellow text in tooltip).