I maintain a wordpress site using the wpdiscourse plugin. Once you create a user in wordpress, go back and edit the user. There is a checkbox with the header “Email Address Verified” and a caption Marking the user’s email as verified will allow them to bypass email authentication on Discourse. After clicking on this checkbox, our login issues for new users disappeared.
We are using the discourse.org hosting option. If you look at the Enable Discourse Connect setting in the Discourse admin panel, it says “Enable sign on via DiscourseConnect (formerly ‘Discourse SSO’) (WARNING: USERS’ EMAIL ADDRESSES MUST BE VALIDATED BY THE EXTERNAL SITE!)” I believe the warning is referring to the checkbox referenced above.
Hope this helps.