Check out this Super Smash Bros. Ultimate guide on which points of the game you can't return to and more!
Points Of No Return In SSBU
There Are No Points Of No Return
There are no points of no return in Super Smash Bros. Ultimate. You can replay everything, including Adventure Mode, so there is no need to watch for certain points in the game.
Stats & Records Are Permanent
Your account's stats and records in all game modes are permanent and can only be reset if you delete your save file and create a new account.