Is there a way I can edit the glitch project with other text editors than vsc (for example notepad++)?
nope, but you can code one! ( an addon for glitch for notepad++)
If there is a way to export from Notepad++ to GitHub, then we could import that into Glitch from GitHub.
For the export to GitHub part, this topic should do: https://stackoverflow.com/questions/10383837/github-notepad .
Yes there is actually; all these answers are wrong; Glitch allows you to upload you git repository to glitch: Custom Fonts in Discord Bot