please update fontconfig
an update of fontconfig made gtk3, webkit and vte (including in gtk4) use colorized font antialiasing (it did not affect gtk4 widgets because it is not supported in 4). this has since been fixed upstream, but flathub and gnome-nightly flatpaks are still using the buggy release.
please update it, the rendering can cause physical dyscomfort on the eyes and is not consistent with the modern gnome look