SanDisk, Apple and IpadPro No Go

We have several apple devices - iPhones, ipads, minis, pros. I wanted to put all of the photos that are on the phones - especially the really old phones - as well as the photos on a few thumb drives - on to a single item. So I got a SanDisk drive to do just that and spent a LOT of time getting all the photos moved over to it. I’m not the most technically capable person, but thought this was a great option to save - in particular -our overseas trip pictures. Aside from this arrangement I now save current photos to amazon prime. I’m still having difficulty understanding the Apple Icloud option. So I wanted to view my old photos that are now on the SanDisk thumb drive on my new iPad Pro. It’s a larger device and I can download items directly to it if I need to. I could also mirror the photos using Apple TV if I just wanted to look at them on an even larger screen, but that doesn’t solve my problem. So I searched around the Apple website for a connector/adapter and couldn’t find anything. During our morning walk at the Mall this morning we stopped at the Apple store to get some hands on advice. But, this didn’t work either. They said what they have may not be compatible with the SanDusk thumb drive but I could buy one and return it if it didn’t work. I’m not really sure why it wouldn’t but decided not to bother. I do have a work around but it is annoying. I really like my iPad Pro and Apple Pencil, but I really hate the connection port. So I’ll spend more time searching for a solution. There’s got to be something out there that works? Any thoughts?