I have noticed Inkopolis Square being without color, so Splatoon 3 might actually carry on the tradition that Nintendo has been doing for the Switch generation: Town building/restoration. What I mean is that they have done this in Breath of the Wild as a side quest as well as in Kirby and the Forgotten Lands.
Basically, little by little as you progress through the story of Sider Order, Inkopolis Square will be restored, however, I don't think the Jellyfish will be doing the restoration of Inkopolis Square, even though they are the ones who we see are in charge of the construction-related things. Instead, I think it's going to be the Octarians that you might have to rescue during Side Order. Why I think this is because Octarians always repurpose things that were left behind, like the domes that humans left behind or the signs and other things in their weapons.
Basically, little by little as you progress through the story of Sider Order, Inkopolis Square will be restored, however, I don't think the Jellyfish will be doing the restoration of Inkopolis Square, even though they are the ones who we see are in charge of the construction-related things. Instead, I think it's going to be the Octarians that you might have to rescue during Side Order. Why I think this is because Octarians always repurpose things that were left behind, like the domes that humans left behind or the signs and other things in their weapons.