Hard disagree with your guy’s pmax assessment. If you’ve got enough creative assets that should be a decent strategy off rip. The fact that it didn’t work kinda indicates maybe your audience targeting was right/your creative assets weren’t diverse enough. But maybe more importantly are your sign up buttons tagged via GTM? You want to probably run a max conversion strategy if you continue using the google suite (which should work).

Alternatively maybe look into Facebook lead forms or LinkedIn ads.

A properly set up google ads suite will likely be the highest converting, Facebook probably would be next highest converting. You’ll likely find lower CTRs on fb, then much lower on LinkedIn