I have adopted an Umbraco site and fairly new to the content management. We need to add some data to a menu (snippet and an image) to make a mega menu. Currently it's a bootstrap menu running a loop for pages that is visible and has the child pages as part of a dropdown menu. What would be the best approach as there is no "menu management" - I would like to add a short blurb to each dropdown menu along with an image - I'm struggling to figure out how the best concept would be

I would add this to a composition and that composition to each page type you can have in the menu

Or you can look into a menu-management package (ex: https://marketplace.umbraco.com/package/our.umbraco.simpletreemenu) which allows you to create your menu configuration in a separate are of the tree (eg a "Settings" node) You can then define any properties needed for each "menu item". If you want to "auto-generate" the nav based on adding content nodes, then @Matt Wise has the right idea for you. You can also consider a combination of the two, which is something I've done before.