> The problem with that is that (nearly?) every GUI toolkit is object oriented
Except for things like React which are more or less functional reactive programming, but in case of react its stateful. Functional reactive programming exist, and GUI is not obliged to be OO
clojure was introduced in 2007, there have been many GUI toolkits that have been implemented entirely from scratch in other languages since then. QML+QtQuick, Dart+Flutter, Nuklear in C, Nana or neoGFX in C++, etc etc