I had a flight like that where FA looked overwhelmed. This was way before the pandemic, I was in F on a 738 flight.

Before takeoff, this FA had a problem starting a safety video in IFE, did not know how to operate, and needed help from other FAs. This should have been a hint. During the flight, the drink service was very slow. The FA looked as overwhelmed or his mind was elsewhere. The FA was pleasant, not rude or indifferent. During the meal, the FA asked for a choice but hand out the wrong one. At the landing, the hump of touch down, a shelf door in a galley popped open and cans of soda and juice came rolling out. Once the aircraft was on a taxiway, the FA stood up from the jump seat and with his foot rolled cans to the corner of the galley. For a few cans rolled into passenger seats, this FA did not bother and acted as if nothing happened.

I remember on another flight, CRJ-700 in F. The FA did PDB, a British gentlemen across the aisle from me asked for Scotch, neat. The FA gave Borbon, the British gentlemen kindly mentioned to the FA that it was Borbon, not Scotch. The FA did not know the difference between Borbon and Scotch. At the takeoff, a door of the cart in the galley popped open and the cart itself started to slide out. It was CRJ so the FA could reach the cart from the jump seat sitting down. The FA hold the cart till we were leveled off enough that FA could stand up from the jump seat.

I think in both situations FAs were rookies. I think most rookie FAs do just fine, but once in a while, there are rookie FAs who are not ready for a prime time yet. These two flights were memorable enough for me that I still remember.