How to change size of ALL icons/folders in Finder? I only know about this:

defaults write com.apple.finder DesktopViewOptions -dict IconSize -integer 188x188px.; killall Finder’


But it’s only for the Desktop…
Open a Finder window in Icon mode (⌘1), then click Show View Options (in the View menu, or ⌘J). Make the changes you want, then click the Use as Defaults button at the bottom of the panel to make it stick for all folders.