Hey dev here. The only reason a device ID is recorded is for push notifications. The source code for this is available at https://GitHub.com/memmy-app/memmy-push. We need the push notification token for your device (unique to the app actually, and I’m not fully confident the privacy notification is required but because Apple can be anal, I added it)
If you do not enable push notifications then no data is transmitted to us at all. Everything stays on device.
Also, here is the code where this data is transmitted to Memmy's server https://github.com/Memmy-App/memmy/blob/e67ce00ec8dcc4897bf9740478594cf72fbbe3f2/src/hooks/notifications/useNotifications.ts#L59