After having activated the new dashboard page, I am unable to find a way for setting the icon size. With the old design, there were buttons with S, M and L at the bottom.

I stumbled upon this by accident after my icon size was reset to the default somehow. To reset this to the desired size, I had to temporarily disable the new dashboard, change the setting on the old page and then return to the new page. This does not really feel correct, as there should be a way to change this with the new build page as well.