This shortcut will shorten a URL you pass to the shortcut as an input or a URL you have on your clipboard.

This uses the TinyURL site to shorten the URL instead of the Gallery's Shorten URL shortcut

After the shortcut runs, the output result is the shortened URL, which is copied to the clipboard and also is the output of the shortcut if you are running it as a "Run Shortcut" action within your shortcut.