I am looking for an open source SMS app for Android that can mute the contacts that I specify. I want to avoid being shown notifications when I receive SMS from particular contacts. However, I still want to be able to read the SMS from a muted contact when I open the SMS app. The app should run on Android 8.1 or later.
QKSMS can do this. It is available via the Play Store and F-Droid. QKSMS is able to disable notifications for someone with whom you have sent or received at least one message. To disable notifications from a particular person, view the messages from that person and tap on "kebab menu" (three vertical dots), where you will have an option to customize notifications for that particular person.