Ctrl + Tab not present in Keyboard Shortcuts, but works
It seems there is no place one can find an up to date keyboard shortcut list.
Built in Help explains how to open a New Tab via shortcut, but not New Window or New Incognito Window.
A search in DuckDuckGo offered me this page: https://help.gnome.org/users/epiphany/stable/keyboard-shortcut.html.en It contains a lot of shortcuts, but not a New Tab shortcut.
Also I tried different keys and found that Ctrl + Tab switches to next tab and wraps at the end, this is not stated in the built in Help or linked above page.