Here's an only one coffee reply.
It's not something that will ever ever be addressed by Samsung, because it's not a Samsung issue. It's something in your Settings (System or App), that is causing this to happen.
You can try Booting into Recovery and Wipe Cache. You can check the Settings in Spotify (if you're certain that it's Spotify that is playing on Boot).
I know that some music players will play automatically if headphones are connected.
It's definitely NOT a Samsung OS issue.
You can try opening Samsung Members app & Click on Support & Scroll down to Error Reports & Send an Error Report to Samsung... BUT I don't know if the issue will be caught by an Error Report as it is happening just after Boot.
Maybe I'll have some more ideas after more coffee ☕ ☕ ☕ lol 😂