How to get at WhatsApp raw media files? Old phone, app won't let me

In short: I moved from iPhone to Android a few months ago, and now I fear I've lost audio and photo files in the WhatsApp installation on my old iPhone. I have an iPhone that is old and no longer my primary phone. When I tried to move WhatsApp to my new phone (Android) it copied over text messages, but not audio messages and photos in chats. For a while I could open WhatsApp on my old iPhone and see these old chats with their media, even though I was not getting new messages in that instance of WhatsApp. So I thought they were safe - at least saved. Now it has decided to lock me out of my own data. When I open the app on iPhone it says I have to link new phone, when I do, it doesn't show the old chat histories with the media. I thought it did this once before, and I feared it deleted my media, but then I saw them again (months ago, can't remember how). Is there a way to get at the raw files so I can copy out some photos and audio messages? When I connect my iPhone to my MacBook, it shows in the Finder sidebar. I click there and there is a tab for "Files", but WhatsApp is not listed among the apps.