Circuit ratings in North America are based on intermittent, not continuous, ratings (Europe uses continuous). Cont = int * 0.80, int = cont * 1.25. A 50A circuit in NA is an intermittent rating. The continuous equiv is 40A.
Breakers have a time curve, and will trip if you draw more than X for Y seconds. For a 50A breaker, X is 40A for >3hrs (definition of continuous load), X=50A, Y=a few seconds, and X=a few hundred amps (short), Y=0 sec.
You might think that "well, I'll only charge for 1 hr. That's less than 3hrs, so it doesn't meet the continuous rule, right?" But the NEC says that any EV charging, regardless of duration, must be treated as a continuous load.
EV charging is the most "stressful" thing you will likely encounter in residential environment. Pretty much everything else falls under the intermittent loads (even heating elements generally cycle on and off).
Expanding on this, 6ga copper has different ratings at different temps (all ratings are intermittent). 60 deg C = 55A, 75 deg C = 65A, 90 deg C = 75A. You can only use the lowest degree C rating for all components in the circuit. For residential, that's either the 75C ratings of your breaker, or the 60C rating of romex. THHN in conduit is good for 90C, but your breaker terminals aren't, so you would be limited to 75C=65A with THHN.
You are allowed to round up the rating for non-standard breaker sizes (so a 60A breaker on #6 romex, 70A breaker on THHN/conduit), but that's only for the breaker, not the circuit rating as a whole - the wire is still the limiting factor.