You should consider adding a "pushing" effect to keep the player in the play area, forcing the player to walk back before they reach the invisible wall. That would probably make it more clear that the player isn't supposed to leave the city. Super Mario Odyssey does something similar in Seaside Kingdom, for example.
The UI doesn't work well on an ultrawide screen. Maybe try locking the UI elements to a 16:9 box no matter the screen width? Not a huge deal, I just set the game to run in 16:9 in the settings and it was fine. I assume you simply do not own an ultrawide screen.
The core gameplay is rather fun, with a Katamari-style appeal, but there isn't really much replay value. More levels and a singleplayer mission mode would be great, but obviously a lot of work. Perhaps consider having the player start smaller for those as well, so there's a buildup from destroying small things to big things; that's always been my favorite part of the Katamari games.
The art style and character designs are very cute. I love the little bits of text on the billboards and character descriptions as well; small details like that are always adorable.
What you've made so far here is amazing! Keep it up!