From https://delta.chat/en/help#sealedsender
Does Delta Chat support “Sealed Sender”?
No, not yet.
The Signal messenger introduced “Sealed Sender” in 2018 to keep their server infrastructure ignorant of who is sending a message to a set of recipients. It is particularly important because the Signal server knows the mobile number of each account, which is usually associated with a passport identity.
Even if chatmail relays do not ask for any private data (including no phone numbers), it might still be worthwhile to protect relational metadata between addresses. We don’t foresee bigger problems in using random throw-away addresses for sealed sending but an implementation has not been agreed as a priority yet.
Florisboard. Android keyboard, doesn’t have spell checking yet but I’ve been using it for years, you might not need autocorrect as much as you think! (Note for Samsung users: Samsung Keyboard keeps adding items to its clipboard history whether it’s default or not. Clipboard history is also accessible through Edge Panels. Your passwords might end up and sit there for a long time… you can use adb to disable com.samsung.android.app.clipboardedge and com.samsung.clipboardsaveservice.)
Delta Chat, for messaging. Sign-up is extremely easy using the default server, and I’ve convinced some of my contacts to join.
I suggest mega.io as replacement for OneDrive. I use it myself, and it has a desktop app like OneDrive’s.
It turned out to be… Samsung Keyboard in the end, probably reinstalled itself after a system update.
I thought it’d be something like com.samsung.clipboardsaveservice, which was the culprit on my old phone, but it didn’t even exist on my new one.