Can a menu link go to another website and open in a new tab?

You can add the link, but at the moment it opens in the same tab. Go to Settings → Appearance → Layout Settings and open the Menu tab.

1. Pick the menu in Select a menu to edit.
2. Under Add menu items, open Custom Link and fill in Link Text and URL, both required. For another website, enter its full address including https://.
3. Click Add to Menu.
4. Drag it into place under Menu Structure and click Save Menu.

Each item also has an Open link in setting with a New tab choice, but the storefront menu doesn't apply it yet, so the link opens in the same tab. If a new tab matters for this link, contact Wcart support.