To install fonts, you need to get the font files and copy them to the fonts folder located at ~/.local/share/fonts/. The .local folder in in the Deck’s home directory, but it’s hidden by default so you’ll need to turn on “show hidden files” in the file explorer menu. If the fonts folder doesn’t exist already you can create it. After the fonts files are installed to the folder, reopen your applications and the fonts should show up.

As far as getting the font files, that’s a lot harder. The AUR package people usually use to get fonts actually is downloading part of a windows installation iso and ripping the fonts from that. If you have access to any windows PC, you can copy the font files from C:\Windows\Fonts and use those.