Mii Fighters are tied to the local emulator system profile rather than just the game save file. If your selected save file had custom Miis, they might not port over seamlessly unless the user profile configuration matches perfectly. You can easily recreate these manually in the Games & More menu.
Enter the for Yuzu . This single file transforms your game instantly into a fully completed copy, allowing you to access every fighter from the very first boot. super smash bros ultimate 100 save file yuzu link
Play naturally for 10–15 hours to learn the basics. Then install the 100% save file to unlock the remaining 50+ characters you don't have. Mii Fighters are tied to the local emulator