Hello martin4307, if it helps you on one of the sites I made a very simple modification. When a user registers they are already warned. Maybe it can help you, it is as simple as adding a message in the language folder.
The path is yourdomain / language / en-GB / en-GB.com_community.ini
Locate the constant COM_COMMUNITY_REGISTRATION_COMPLETED_NEED_APPROVAL = A verification email has been sent to your email. Please verify your e-mail address. And add the sentence "example" If you don't see your activation email in your main inbox, please check your spam folder. "
The result on the screen is https://prnt.sc/w0rhc0
You can do this same action from the Joomla panel in Language / Create a new modification and in the text area add the last sentence.
You can see it here https://prnt.sc/w0rkk5
This modification from the Joomla panel is undoubtedly the best option, it will not be removed when you update JomSocial. Greetings and if it has helped you, I will be delighted.