Press the power button to turn on the Mac or wake from sleep. Press and hold the power button for 5 seconds without lifting to force your Mac to turn off. Press and hold power button for 1.5 seconds to get the turn off dialog. This dialog will ask if you want to restart, shutdown or put the Mac to sleep. Change System Settings to Prevent Spotify from Opening on Mac Startup. So basically, your system keeps the log of apps that automatically open during the startup. This log might be pushing your Spotify app to open during every boot. All you need to do is remove Spotify from the list.
When you log out of your Mac or restart it, deselect ”Reopen windows when logging back in” when prompted.
Or start up in safe mode, then restart normally. This doesn't change the setting, but your Mac forgets any windows that were open the last time you logged out or restarted.
If you deselect this setting and an app continues to open automatically:
To prevent apps from remembering the windows they had open, choose Apple menu > System Preferences, click General, then select ”Close windows when quitting an app.”
Or press and hold the Shift key while opening an app. This doesn't change the setting, but the app forgets any windows that were open the last time you quit the app.
If these steps don't work for an app, the app might have its own setting for reopening windows. Check the app's preferences or documentation, or contact the app's developer.
Or use Startup Manager as your Mac starts up: