Monthly Menu
you can only minimize it not get rid of it.
Unfortunately the achievement list is a permanent part of the UI. (After you unlock it through levelling your first character.)
You can minimise it. Or you can pick any achievement (dailies, monthlies or the permanent ones) and add it to your watch list by clicking the eye symbol and then only that achievement will show on screen. Pick something you’re working on to track it, or pick something you don’t care about so you can ignore it.
Alternatively if you complete the daily and monthly achievements the list will disappear, but only until the next day.
“Life’s a journey, not a destination.”
Complete it, then it will go away
Actually if you’re new and have a low-level character that may be harder to do, but you only have to get 4 of the categories to complete it, and you might find it fun to have a go at 