Does the resolution take a dump on zoomed?
Standard. Zoomed is for old people.
Does using zoomed diminish the resolution of the iPhone Max?
I’ve noticed it blows up the wallpapers also.
Not that I've noticed. Wallpapers can be adjusted as well.
Are you using bold or increased text size also with the zoomed feature?
I use standard on my 6s Plus. On the Plus, there's a big difference in the app icon sizes. On the Max, the difference doesn't appear to be that much. Not on the screenshots I've compared. They're slightly larger on zoomed, but not by much.