I installed several custom fonts, by downloading them, then double clicking the .ttf in the file manager, then install in the font manager when it opens. Then in the terminal and I went to
menu → preferences → my-profile
and ticked "custom font" but in the drop-down menu none of my custom fonts appear.
I just upgraded from Ubunutu 18.04 to Ubunutu 20.04 with Gnome 3.36.1
The fonts appear in GIMP and InkScape