If I had to guess, a lot of memory usage for GPU based renderers is fonts, and retaining the glyphs as bitmaps and vectors in memory for multiple sizes.
Winner is... QT! 50MB of memory with two textboxes and labels.
I bet this is because QT uses shared libraries and can share a lot of things with #KDE I'm running.
I used this: https://github.com/KDAB/cxx-qt not sure how ergonimic it is with Rust yet, but it runs.
sudo dnf install qt6-qtbase qt6-qtbase-gui qt6-qtbase-devel qt6-qtdeclarative-devel
cargo build --release