It's called Wayland, it took some time to make and next week, new Fedora is coming out that uses it by default (until now you could "only" opt-in during login).
[1] Except Ubuntu, they have their own NIH solution, of course.
Title bars are up to compositor (it was up to window manager in X11). Even client side window decorations (i.e. mostly title bar combined with toolbar) are nothing new, if that is what you mean with custom implementation of window titlebars.
I'm sorry to say though, that I don't remember how I did it, since I've been using mainly macOS and Windows for quite some time now.
My solution is to organize myself so that I don't have to move windows around. I mostly need browser, terminal and emacs. I open chrome in one monitor with specific scaling option, and when I move emacs or terminal around I manually decrease font size with Ctrl-+/-
All these things disappeared when I changed the external monitor for a HiDPI one.
