It's unfortunately a valid "defeatist" point that I hate finding myself falling back into over and over on so many issues. It shouldn't be so hard to say 'yo can you stop taking advantage of me for personal financial gain in every possible scenario'?
Unless it's for a position where that's the standard, e.g. certain investigative journalism roles, I'd call it a red flag and have the scam sirens blaring. Although as a cybersec professional I'd be VERY curious to see where it goes and what their deal is. I'd MAYBE expect some security roles to request E2E encrypted email comms at a certain point in the hiring process depending on the project, there shouldn't be anything discussed pre-onboarding that necessitates using Signal.