Is there is a way to convert a tab into a page…(or do I have to manually recreate the existing tab as a new page)?
There’s not a built-in way to do it. You will need to create a new page, but this would be a great Feature Requests that I’m sure the community has already asked for.
You could clone the page from left menu, then remove all other tabs. Not ideal, but quicker than recreating if you have lots of data in it.