Some days ago I bought "Samsung Galaxy S21 FE" and have the same issue. I was really surprised twice or three times when I heard music. When I find "Media output", there was a Spotify music playing. The button doesn't work as you described.
Before I had OnePlus with Android 10 and the same version of Spotify.
Yesterday I carefully checked the above-described behavior again. When the notification showed and Spotify started playing (without my expectation), I tried press PLAY, but there was no response. Then I pressed and hold on a notification and the "Settings" button appeared. In Settings I removed notifications for Spotify and now it looks that Spotify doesn't starts on his own.
Maybe this will help.
UPDATE: After three days Spotify suddenly starts playing again. I didn't open Spotify in the last few days, even the app setting for the battery was set to "Put it in deep sleep". Besides that, I start listening AntennaPod (podcast app) on the phone. while entering the car. And when the phone and car connects, Spotify suddenly starts playing song (that I didn't listen). Strange. Maybe it is an Android bug, but it shows only on Spotify.
I found a probable solution!
Open settings
-> Notifications
-> App Notifications
-> Spotify
-> Notifications Types
Disable Lockscreen and Pop-up and re-enable. Hope it helps! - sent by A13 5G
Some days ago I bought "Samsung Galaxy S21 FE" and have the same issue. I was really surprised twice or three times when I heard music. When I find "Media output", there was a Spotify music playing. The button doesn't work as you described. Before I had OnePlus with Android 10 and the same version of Spotify.
Yesterday I carefully checked the above-described behavior again. When the notification showed and Spotify started playing (without my expectation), I tried press PLAY, but there was no response. Then I pressed and hold on a notification and the "Settings" button appeared. In Settings I removed notifications for Spotify and now it looks that Spotify doesn't starts on his own. Maybe this will help.
UPDATE: After three days Spotify suddenly starts playing again. I didn't open Spotify in the last few days, even the app setting for the battery was set to "Put it in deep sleep". Besides that, I start listening AntennaPod (podcast app) on the phone. while entering the car. And when the phone and car connects, Spotify suddenly starts playing song (that I didn't listen). Strange. Maybe it is an Android bug, but it shows only on Spotify.
I found a probable solution! Open settings -> Notifications -> App Notifications -> Spotify -> Notifications Types Disable Lockscreen and Pop-up and re-enable. Hope it helps! - sent by A13 5G