This tutorial will demonstrate how you can download font files from the internet and add them to your Monogame projects. Make sure to credit the user and check the licensing agreement.
There are a number of great websites with free fonts for you to download. Make sure you consult the licensing agreement before using anything. Especially if you intend on using it to make money.
Font Space: https://www.fontspace.com/
Good source for 16 bit fonts
Lots of categories
DaFont: https://www.dafont.com/
1001 Free Fonts: https://www.1001freefonts.com/
FontTesk: https://fontesk.com/license/free-for-commercial-use/
There are countless other sites. Use an internet search engine to find what you are looking for!