One of the biggest annoyances so far in SSBU is the fact that in between rounds of Smash, your character choice is seemingly reset, and you are forced to re-select your character. This is annoying when I want to practice vs CPU players, because it becomes increasingly infuriating to have to re-select the character and his costume every single game.
Obviously, I'm pretty sure that previous titles, especially Brawl, remembered your fighter choice in between rounds. Now I've looked throughout the options and I can't seem to find an option to stop the game from forgetting which character I'm playing. I know this is an issue specifically on what I play, because the game will remember my pick for the CPU character, but not for the player.