I’ve been using Image Shrink on Android for the better part of a decade. It works flawlessly for exactly this situation.
I set the resize options to maximum dimension of 1600px.
Then the workflow is share from any app (like the Gallery) to Image Shrink, it resizes the photo(s), then reopens the share prompt to share on to wherever you’re trying to send them (like an email client).
You can also choose Image Shrink in the file picker to do it in reverse - select the files in the app you want, and they get resized on the way in.