Hi @Jakob12
As Dash fires the callback independently (I mean not in a sequential way) I think you can manage to show something that takes the entire screen and at the same time run the other callbacks with other layouts, at least if you are not using different pages: one page for only the welcome page and other for your dashboard.
You can manage to show an introduction message for the entire page using Spinners with full screen, but will be showing for the time the page is loading only.
I’m also trying to manage an other solution like you here: Improving app first loading presentation