Increasing Icon Size in ArcaOS 5.0
ArcaOS 5.0 cames with a functionality called "Dynamic Icon" that allows you to increase the size of icons which was limited on OS/2 Warp.
Increasing the Size of all Icon in the Desktop (Default Size)
To increase all the icon size at the same time of all the icons in the desktop go to "System Setup - Workplace Shell".
On the "Workplace Shell" settings go to the "Icon Size" tab and select "Dynamic Size" and set the required icon size. On my case I'm good with 60x60px.
Notice that you changed that to the "Icon View". ArcaOS (and OS/2), also has a "Tree view" which I also recommend to increase the size.
Go to the text tab page (Page 2 of 2) by click "+" and also select "Dynamic Size" and set the required icon size.
Now your big resolution desktop will look with more comfortable size icons.
Also check the "tree view" and you will see it also has bigger icons.
Checking the Desktop
You can also check if the "Dynamic Icon" feature is enabled on the desktop. Just make a right click and select "Display - Dynamic" and check that it is enabled.