Looking to take a fixed screenshot at intervals while changing the page in safari for a book I am trying to screenshot all the pages of a textbook i have online. I am opening the book in safari, all i want is to automate in some way the ability to take a fixed location screenshot at intervals save it to downloads or desktop(wherever) and then have a my cursor click the next page button and retake a screenshot a multitude of times would this be possible in anyway?
You can do this with the new screenshot key command -  Cmd ⌘   Shift ⇧   5  set to 'Capture Selected Portion'.

Once set, it will capture nominally to Desktop, each titled ScreenShot date/time [eg ScreenShot 2021-03-15 at 4.42.15 pm, so they will file alphabetically. You can capture using Return/Enter or by clicking the Capture button. The selection area is remembered between snaps.
You could potentially automate this, but it's a swift process, so I doubt you'd really need to.
If you need to change the file save location, see How do I change the location of macOS screen captures?