For example, Acrobat can neither copy/paste nor search for any of the following characters:

Ψ (psi), Φ (phi), † (dagger)

For example in this document (also attached to this post for convenience): https://arxiv.org/pdf/2102.12560.pdf?download

I'm guessing it's all Unicode characters? But I haven't tested that thoroughly enough to know if that's precisely right. Regardless, this issue arises daily for me (mostly because of the Greek letters).

I only tested 3 other PDF readers, but none of them have this limitation: macOS's Preview.app, Chrome's PDF viewer, Safari's PDF viewer

It would help me a ton if Acrobat let us copy/paste and search those characters.