I like it too. Checked it out on the nightly flatpak build. Gotta say its unusual to have the hamburger menu on the left instead of the right, but its one of those things you get used to.
~~I also hope the leftmost corner gets to have a button, since it looks too empty there. Ive read theyre considering adding a "global search" button~~ Testing it, ive realized thats where the "copy/moving files to..." circle thingy shows up.
I also noticed when shrinking the window's width the sidebar collapses way sooner than before. This is bc of the search bar not using the whole headerbar anymore, so it collapses the sidebar in order to maximize search bar width