Add your own - not meant to be entirely serious but equally these are things I've noticed to be wary of since starting dating again.
Overly apologetic about being away from their phone. I'm feeling sorry for the men who are profusely apologising for not messaging for a few hours, what type of partners have they had previously that they're so conscious about accounting for their every move? Red flag, potentially not over their relationship or has issues they're carrying over
No sense of self. By this I mean they want to be in your pocket 24/7 or don't seem capable of being on their own.
There are more I'm sure