He used Windhawk for the alt-tab switcher, and you can use patched uDWM.dll's from here for the titlebar buttons that are combatible with later Win10 versions, however Aero Glass works on 1909 max so keep that in mind.
This theme is great, I've been searching for this for years now! However there's one small thing that really annoys me, it's a corner bug on inactive windows in the dark variant of the theme, it looks just fine in other variants. If you can update the theme not to include it, it'd be really appreciated!