Thanks! As I thought. Long lived sticky foreground notifications tend to annoy folks from my experience. Have you seen complaints?
At least I replaced the one from my Matrix client with the UnifiedPush-enabled ntfy. Hopefully it'll replace Signal too at some point. KDE Connect? Why not. K-9 mail? I hope, but that would require JMAP or IMAP adjustments.
One option would be to install the distributor as a system app.