Hi Charlie.
I do not know if you’ve tried this solution.
Unpack the attachment and place the gtkrc file directly in the home directory (where you have other files with configuration, eg gimprc, pluginrc, etc.).
In line 4, I can edit the font and its size.
Tested only in Windows.
Checked for Gimp 2.10 - but it does not work for GMIC QT (because it is not based on gtk).
gtk-theme-name = "Default"
style "user-font"
{
font_name="Arial Bold 14"
}
widget_class "*" style "user-font"
gtkrc.zip (202 bajty)