In my opinion the difference is that "behaving in a socially expected way" is following norms so that no bad attention is drawn to you or to prevent others from having negative experiences from your behavior, and "performing" is the constant feedback cycle of emulating behaviors and traits that you think will draw positive attention and create good experiences with others.

A good example is that most things people do to be polite are considered "behaving in a socially expected way" while interactions like a young adolescent male lowering their voice when talking to somebody they are attracted to is "performing".

Performance is common for many other interactions like dressing up and formalizing language for job interviews, "telephone voice", as well as matching posture and speaking style during interactions. Performance captures the potentially unfounded change in behavior to better a specific interaction. Many sitcoms often create comedic moments when performance for a specific interaction is not compatible with performance for another interaction, so when "worlds collide" (as in Seinfeld) the character has to either struggle with maintaining both performances, or choose one form of performance to stick with and ruin an interaction with some other situation.

For me, 'performing' meant going above and beyond at social events to be the person with a witty one-liner or good observational humour.

It felt fine initially and I enjoyed the positive attention, but eventually it became a chore. No one is funny 100% of the time, and when I started thinking more about "How can i get a laugh from these people next time", that's a sign that I need to re-evaluate what I get out of this relationship.

The feeling should be "I'd like to hang out with these people with no expectations from them or from me" but that's not always there unless you have a specific level of comfort with those people.