One thing that I had to realize in moments like these is to just have fun- the people can wait. We’re not paid enough to give our all when Starbucks isn’t going to help us out the same way. Take your time and just communicate with your team.

You just get immune after awhile.
And because you are new - this is a fresh situation.

I will tell you this - it will get *worse*. Holidays are coming ...

I think what helps me in this sort of situation is that you are the mid and get to leave by the time it hits 4:30 or whatever. Maybe bring up to your manager how challenging it was, and ask how the numbers compared to the morning that same day. If you are having 6 partner plays in the am for 70 customer transactions (per half hour) and only 4 partner plays for 60 customer transactions, then there is something wrong. Considering you have quite a few green beans, it sounds like your store is on the more short staffed side. But maybe talk to a trusted supervisor and say "hey, this green bean needs some coaching, they really struggled under the pressure of the weekend" and point out some things you are noticing in this partner. Do they just not understand what to do or did they get overwhelmed? Is there anything you can do to support them from your position or do they need help from a higher power?

Don't stress my pet the people at the back of the line know what they were getting into all you can do is focus on the 2 drinks infront of you don't push your self todo more than 2 at a time that's when you drop some of your spinning plates you got this your are in control and if someone is going to yell they had planned on doing so anyway it's not your fault all you can do is serve theyre triple blended no ice no foam no fun frap with a smile and if they are mad give them a recovery and move on to the next guy you can do it your are a mighty latte making machine!
Edit: a word

I used to get really overwhelmed when it’s busy and understaffed and now I’ve just learned to not care. Not in an apathetic way but just not to freak out because I know I’m doing the best I can and people are just gonna have to wait and that’s that. What’s the worst that can happen? Pretty much nothing. I don’t think this is very helpful but I know what you’re going through and I understand. It’ll just get better with time.