I use an increased font DPI on my 4k screen (instead of scaling) and this works well for most applications. On Wayland the Gtk applications look ok as long as I run them via XWayland (example: GDK_BACKEND=x11 virt-manager), it sets the same font size of Qt/KDE applications. If I run the same application directly via Wayland, the font dpi seems to be ignored and the fonts are to small (example: GDK_BACKEND=wayland virt-manager).
I'm sorry but this out of scope. Please check how Gtk needs to be configured.