I have the a Formula (Text) field under the Results tab of the saved search. Is it possible to use this column in the Available Filter of the saved search? I tried putting that field as the first field under the Results and Available Filters subtabs. When I tried to use search for some keywords using % in the saved search results, it seems that it's not working.

Yes, there's a way to do this. You have to setup the

Formula (Text)

field as a criteria. Have a read of this, let me know if you have any trouble with it: Using NetSuite Saved Search Formulas as Filters

Wonderful! Thank you!