The max res. is/was to support up to 16:10 aspect ratio monitors.
I don't have a 21:9 monitor or TV, you'll have to see which, 1440 or 1080 option is more suitable for you.
Netflix I also do not have, so can't help with that.
One of the specs I checked was a Dell card, perhaps Samsung support/forum can help with what the monitor capability is with that card, or maybe also Dell support/forum..
Ryzen 5 5600x, B550 aorus pro ac, Hyper 212 black, 2 x 16gb F4-3600c16dgtzn kit, NM790 2TB, Nitro+RX6900XT, RM850, Win.10 Pro., LC27G55T..