When you have 2 Portfolio Pages, and you change one Portfolio Page to 4 columns, the other Portfolio Page will also change to 4 columns.
If you want to use different settings on other pages, you can do these.
#1. First, set the first portfolio page to 4 columns.
#2. Open Portfolio Page where you want to change to 2 Columns and use below tool to find Page ID.
In my example, it is:
- #collection-66a1bfc99041e47b896c1e48
Use this code to Custom CSS to change it to 2 columns.
#collection-66a1bfc99041e47b896c1e48 div#gridThumbs {
grid-template-columns: repeat(2,1fr);
grid-gap: 20px 20px;
}