mutter-rounded VS adw-gtk3

Everything you need is under the install section

For rounded corners I've used Mutter Rounded which is basically a patched Mutter (Gnomes window manager)

Since OP doesn't answer I simply googled it and it seems like OP uses this project: https://github.com/yilozt/mutter-rounded

Good question. The dev himself has said he does use a certain patch in his build. See here.. However, I went inside the code and it appears that he first downloads the Mutter source from RPM (which does not have the performance patches, yet), builds a big "meta"-patch out of everything in the "patches" folder, and applies those changes on the downloaded mutter build. So to be safe, I downloaded 1877 and 2487 manually, and edited package.sh myself. Gnome runs significantly faster, with fewer dropped frames, especially in the overview and app menu. (1877 gave me a few quirks though so you might want to skip that.)

Use this theme

As far as I know it doesn't exist yet... but most likely Evince will be ported in the future. But while that doesn't happen, what you can do is use the adw-gtk3 theme (https://github.com/lassekongo83/adw-gtk3) for legacy applications to combine with applications that are already ported to libadwaita

Why not use the adw-gtk theme for gnome to make all the deco's match rather than use Adwaita-Dark?

Application Theme : adw-gtk-3 with Gradience

You can use the adw gtk3 theme. https://github.com/lassekongo83/adw-gtk3

GTK theme: adw-gtk3

That's because i use this KvLibadwaita and adw-gtk3 themes to have everything looking the same on Gnome :>

Just found a workaround for the issue until an update fixes the issue for Fedora 28 - Alt+F2, type "r" to restart Gnome Shell. More info: https://github.com/lassekongo83/adw-gtk3/issues/213

I believe that adw-gtk3 could still be beneficial in ensuring a uniform appearance across both GTK3 and GTK4 applications. The more solutions we can offer to users, the greater the likelihood of achieving the desired outcome.