Is that application actually doing on-device transcription? Under "Data safety" on the Google Play page it says "This app may share these data types with third parties: Audio" which doesn't exactly instill confidence that my audio will 100% always stay on my device. It also says "Data is encrypted in transit" but if data stays on the device, why it has to be "encrypted in transit"? There should be no transit at all.
Yes, it works completely offline, including transcription and recognition of music. There's an optional cloud sync feature, which I assume is the reason for the notice on Google Play.
I just tested it and it was pretty mediocre at least with my accent. I can definitely benefit from a decent app for quick note recording with a button press->transcribe->upload to gdrive/good UI app for later grepping.