It's possible to renew an F-1 visa while on STEM OPT but there's some risk because a consular officer could conclude that you do not have the intent to return home to Serbia after the end of your STEM OPT. That being said, F-1 students renew their visas while on STEM OPT all the time; it's just not risk-free so you would want to be well prepared for your interview.

Thank you SO MUCH for your response, and for taking the time for this entire AMA, it is very very much appreciated.

I am curious about what the interview might entail? I've applied for tourist and F1 visas and renewals about 6 times and I've never been asked any pointed questions.