When inside the chat itself, there is no notification sound for incoming messages. The messages just show visually, with no audio.
But when outside of the chat, or not in the messages app, the sounds occur when messages come in.
This was the case on multiple Samsung phones, and with multiple different messages apps for SMS/MMS/RCS.
Is there a way to solve this? Couldn’t find any solutions after researching
In my country we mostly use WhatsApp and it has a specific option in the menus that says ‘in chat notification sound’ which does exactly what you are looking for.
What I would suggest is try another messaging app that is more feature rich such as textra. I bet they do a better job at handling notifications than the default app.