Yes, it definitely is.
I hope that the next Ubuntu-MATE will use Calamares as installer, or something else that works. Even a ncurses installer would be good, as long as it works™.
Yes indeed: App Center Glitching - #8 by tkn
It is, just like the installer, based on flutter and just like the installer: buggy.
Probably all due to the influence of GNOME:
No matter if you use Mutter, Flutter, or Clutter. It always ends in stutter. 