I've been having this issue with the top speaker for so long that I don't know what else to do: Every time I restart my phone, the top speaker turns off and the stereo sound won't work. I'm sure it's a software issue because if I use the *#0*# menu and tap on the speakers button it immediately turns on again util the next reboot.
I'm using the last version of Android available (And the problem has been present for 3 or 4 updates now so they don't seem to be working on it)
Is anyone having the same situation?
I would put the phone in Safe Mode which disables the downloaded apps and leaves the stock ones working and then see if the speaker works as it should or not.
If it does then somehow an app maybe causing this so start deleting your most recent apps one at a time until it resolves.
If not then you'll need to use a Samsung Service Centre or go back to the source who supplied the phone to you.
I wish you all the best with this situation.
My advice comes from being a UK Samsung Phone Owner.
I have no affiliation with Samsung.
Current Phone ~
Samsung Note 10 Plus 5G _256Gb >_ Samsung One Ui 2.5/ Android 10.