When a notification is silently updated on Android, it appears on the desktop 
as a new notification.

STEPS TO REPRODUCE

1. on Android 11, open People¹, say “hi” to Cat, minimize app
2. when Cat says “Meow”, press the “open bubble” button in the notification

¹ https://github.com/android/user-interface-samples/tree/main/People

OBSERVED RESULT

The same notification appears on desktop twice. (Opening a bubble results in a 
notification being reposted with setOnlyAlertOnce(true), among other things.)

EXPECTED RESULT

The notification does not pop up on desktop or make sound

SOFTWARE/OS VERSIONS
Windows: 2004 (19041.1052)
Android: 11, LineageOs 18.1; also reported on Android 6
App: 1.17.0 (org.kde.kdeconnect_tp)

ADDITIONAL INFORMATION

There are some ways you can update a notification silently:

* post a notification with flag FLAG_ONLY_ALERT_ONCE, that is normally set 
  by calling setOnlyAlertOnce(true). If the notification already exists, 
  it is updated silently; otherwise, it pops up according to its
  notification channel settings. This is the most “standard” way of
  updating notifications silently on Android, but some app, especially
  those targeting older Android versions, can choose the method below,
  as it allows posting *new* notifications silently.

* post to a notification channel with low importance (< IMPORTANCE_HIGH), 
  no sound or vibration, etc. Telegram, WhatsApp use this.

* before Android O (< API 26), don't set high priority (> PRIORITY_HIGH),
  sound or lights