For NetSuite reports, are we not able to use "and/or" conditions in the Filters section? I'm looking to add (entity is not empty OR entity (line) is not empty) to a report. Is this possible?

yes, in advanced search tick "use expressions"

It's annoying that Reports don't have expression builder like saved search.

I don't see any formulae...in the criteria section of Netsuite Report functionality. The closest alternative that comes to my mind would be to build an Excel Web query on the report (or multiple reports) and build a custom report in Excel that does the job. Clunky for sure, but probably gets the job done. For Excel Web Query, look under More Options on the report customization screen.

All right. Thanks for confirming there's nothing like expression builder in Reports. That's what it was looking like.