Not sure what the issue is but I don’t think you need to upgrade to Ubuntu 20, I run 18 snaps on 20.04.
I have demo Snapcraft Tkinter code if that helps: GitHub - argosopentech/snapcraft-tkinter
Not sure what the issue is but I don’t think you need to upgrade to Ubuntu 20, I run 18 snaps on 20.04.
I have demo Snapcraft Tkinter code if that helps: GitHub - argosopentech/snapcraft-tkinter