After downloading and signing into my microsoft account on the NEW launcher after being prompted by my OLD Java edition Launcher, I started the game and attempted to pull up my saved worlds I have been working on. However after pressing Singleplayer on the NEW launcher I was brought to a 'Create New World' screen and not the list of worlds I have on my computer. I then checked my Multiplayer section and it was as if I had never joined any servers before in my life. I didn't even check my Realms because I started to worry that I lost everything. Checking my computer files I found all my worlds still intact along with their respective data. I started the OLD Launcher and thankfully all my worlds, servers, and realms and data are still fine.
What path were the save files you did have found in? Could you paste in the path, removing any names/personal info, but including the root drive letter you're based within?