Many users seem to miss or are oblivious to deprecation warnings. There are often posts (for example) when an integration’s configuration has been migrated from YAML to the UI or an integration gets deprecated as a whole (among other kinds of deprecations). The notice has typically been posted as part of the release notes, the docs for the integration would state deprecation, there might have been forum posts, and so forth. Still, when the time comes when the removal or change happens, many users are caught out.
My suggestion is to have a UI configurable setting to post specifically deprecation warnings as persistent notifications.
I am aware that users can see errors and warnings in the logs via the UI, but a nagging factor might prove useful.
Persistent notifications are already used for similar purposes, such as login attempt failures.
Note: I haven’t been affected by such changes much, because I make a real effort to stay up to date. I’m mostly logging this based on what I’ve seen. Even so, I’d probably use this feature anyway to ensure I don’t miss something by mistake.