A moderation queue for everyone's first post is among the best solutions if you can minimize approval time. But you need some impressive manpower for that, like

A moderation queue for everyone's first post is among the best solutions if you can minimize approval time. But you need some impressive manpower for that, like mods willing to get notifications for each first post. Right now I post registrations and first-posts to a #forum-activity channel on my forum's Discord.