Fltk is stack-based (no heap allocation) and parents own their children. When a parent window goes out of scope, poof, memory cleaned up.
Fltk is also easy to use. In C and C++ land there’s fltk-config utility that will automagically set compiler and linker flags etc.
There’s a lovely fltk book that the rust crate links to in its extensive documentation.
There are plenty of even lower resource options like littleVGL, which only needs a drawing routine.