If the Settings interface is not working for you, you can try a CSS snippet to set the fonts manually for the time being. e.g.
body {
--font-interface-override: 'DejaVu Sans';
--font-text-override: 'EB Garamond SemiBold';
--font-monospace-override: 'Fira Code';
}
Oh, I see you’ve already edited the .obsidian\appearance.json file manually. That or typing in the exact font name in the Settings UI and hitting Add is also an option.