I was deep deep in reddit and possibly found a solution. I haven't tested it myself yet but going to test it tomorrow.
Quote from reddit:
"1. Disable Discord overlay and messaging notifications"
"2. Close Riot Vanguard (You have to restart pc to play league again"
Found many people that play Valorant/League like myself that the Riot anticheat system "Vanguard" is the most obvious root cause for this Fortnite/Windows freeze that is happening to me and you, and many others.
Also the discord thing might also be true, because some are reporting that closing/quitting discord entirely before launching or playing Fortnite is also making the game playable and not freeze. And the discord notifications can interrupt with the game if you have notifications on.
I can link the reddit thread here also. Its full of like minded individuals with similar problems.