I am also pretty sure it is Xiaomi specific. Having reconstructed the timeline of when this issue first arose, I am almost certain it was triggered by the latest MIUI update (which was from Oct 22, I think, but which I only installed recently). Prior to that I had never had any issues with the camera crashing Evernote (or any other app). I have emailed tech support to let them know that too.
I think I will wait for the next Evernote update for Android and see if that helps. If it doesn't, I will try the fix you suggested. (Thanks for that, by the way).
For now I have a relatively acceptable workaround using Microsoft Lens to scan docs and then share to Evernote, so I'm prepared to be patient and wait for the update. Fingers crossed!