vincebodie Hello,
If the Joomla 4 site already has its own existing users, it's not possible to merge them seamlessly with the Joomla 3 site, as the user databases will be different.
However, if Joomla 4 is a new website, I recommend using Akeeba Backup to create a backup of the Joomla 3 site, restore it on the Joomla 4 site, and then follow Joomla's migration steps to upgrade to J4, including JomSocial.
Let me know if you need further assistance.
Best regards