The idea of the other party needing to setup an account is off-putting to me.

The way I handle this currently is to use https://onetimesecret.com without any added context, just the password string, and then send an email / message such as:

Here are the credentials that you requested:

Username: foobar

Password: https://onetimesecret.com/secret/6usoxihjgv1d (this link only works one time within X days)

You could even setup a separate link for the username, etc.