After a lot of searching I found an amazing program that lets you use Text-to-speech to chat through voice chat in Fortnite and most other games. Here is the link: https://github.com/Wurielle/izabela-desktop
This is the old Reddit thread that tells about it: https://www.reddit.com/r/pcgaming/comments/6opuoc/i_found_and_made_a_way_to_use_texttospeech_ingame/
There are many reasons why someone might want to use text-to-speech in Fortnite, they may not have a mic, or may be mute or have other speech impediments, or it may be a young person or a female or someone with a weird voice that doesn’t want their voice to be the center of attention, or it could be someone who plays late at night when other people in the household are asleep so they can’t speak out loud then. I searched a long time and didn’t find a good/convenient solution until finding this program. Check the links, it is all explained and it is easy to set up!
Good luck and have fun out there, hope this helps someone else too!