3840 x 2160 vs 5120x1440

Today, I'm going to need your help.

I have a PG32UCDM(Amazing monitor by the way) But watching videos on Youtube and reviews of ultrawide monitors, I am ready to make the jump to a 32:9 (to be more exact,the 49 inch MSI monitor) but first I have a few questions:

Going from 3840 x 2160 pixels to 5120x1440 is an interesting pixel drop,Is the resolution "downgrade" noticeable?

How good is HDR on this monitor?

It is worth noting that I have a 5080 Asus Tuf.