Setting two tabs to split view in one action when using safari macOS catalina
If you have two safari windows open (command + n) then you can press long on the green button on the top left of one of the two windows and the following window will appear:



Then you can choose where you want this page on your screen, left or right, and then on the other side where you selected you can choose the other safari pages. There are keyboard shortcuts for what I don't know ... But a little less expensive than your version