Another important hint: If you change the font size and there are problems with the layout, then restart WSJT-X once. The automatic switching of the button width requires a one-time restart of the program!

I have just tested this again. It works fine on my computer. I personally use "MS Shell Dlg 2" as font. I can set for example 8 pt or even 16 pt and after the said restart the GUI scales as it should. See the following screenshots:
https://sourceforge.net/projects/wsjt-x-improved/files/WSJT-X_v2.6.0/Tests/WSJT-X-2.6.0-rc1_with_8pt_MS-Shell-Dlg-2.jpg
https://sourceforge.net/projects/wsjt-x-improved/files/WSJT-X_v2.6.0/Tests/WSJT-X-2.6.0-rc1_with_16pt_MS-Shell-Dlg-2.jpg

73 de Uwe, DG2YCB