Them: "Could you send the password in an encrypted mail?"
Me: "Yea sure, what's your GPG public key?"
Them: "What's that? Can't you just encrypt it?"
Me: "Nvm, do you have Signal?"

Them: “What kind of signal?”

S/MIME is also a possibility... :)

Should've just encrypted the mail using a random key, see what that does

I've walked friends through generating an RSA keypair through browser-based but client side services and using it to secure very sensitive information in the past. Only patient or paranoid people are willing to use it though, and they are typically also willing to set up GPG

Snowden uses signal

Take a look at yopass, solves this very nicely imho