At that big a size and at that price point, you'll be seeing a lot of monitors with roughly the same advertised specs. Actual performance is another animal all together.
1440p is the sweet spot for for resolution. The Hz of the panel is how many frames it can produce per second. So a 144hz display maxes out at 144 frames per second. A 120hz display, 120 fps, and so on. Response time is measured in how quickly the pixels can change, usually any "gaming" display is going to be 5ms or less. But remember manufacturers can put anything on the box and budget brands often overpromise and underdeliver.
But the thing to look out for with monitors, in my experience, are black levels (how black is the black in a scene), light bleed (is there a lightly aura coming out from the sides), and ghosting (is the picture fuzzy when there's a lot of movement in gaming).
Another note is at this price point HDR capabilities are going to be pretty rough and honestly probably not worth turning on at all.
Other nice stuff to have is an adjustable stand (if you're not mounting it on some contraption).
One more thing to look at is if you're interested in ultrawide. If you do any office work on the computer, ultrawides are pretty damn nice as you can put documents and webpages side by side more easily on the one screen. But ultrawide support is not universal, in games or video, so a normal 16:9 ratio is going to display most content, especially videos, at their native resolution the vast majority of the time.
Now with all of that rambling done, this would be my default pick. Dell usually has good panels and decent quality control. This model is a few years old, but should still check every box you've listed and stay under budget. But keep in mind this is a 21:9 display, not 16:9. I think that's far more suited for a 34 inch size.