Great idea!
Tkinter always looks a little dated and PyQT is more than my brain wants to deal with when I need a simple GUI.
It doesn't have to, it supports theming and there are even themes that use the native GUI.
e.g. https://wiki.tcl-lang.org/page/List+of+ttk+Themes (search for “native”)
I think Tk widgets are themable.
"A little"... it's straight outta the '90s. I am as nostalgic as anyone but even I don't particularly long for that æsthetic.