Ah, the Gramps specific widgets issue. I admit that I often have to reset the Glade preferences, somehow the configured path in those preferences seems to override the environment variables. But if I get the env vars set correctly, and I get the Glade catalog paths in its preferences removed, I can use Glade to fully edit the files on my system. Even on my Python 3.8 installation. In fact I usually use the Glade editor from that installation as it also has the much more up to date Gtk (and Glade editor) v3.24.14.
Even without that, changes not related to the Gramps widgets can be made with the Glade editor. The XML related to the widgets will not be changed unless you directly edit one of those widgets.
And of course, you can always edit the XML .glade files by hand or with an XML friendly editor. I often do that to eliminate excessive changes made by the Glade editor when preparing a bug fix, as the automatic rearrangement of XML sections and other small changes is not really relevant to the fix.