The buttons serves different purpose and long press is not discoverable.
For the rest the button was not supposed to be available for cover buttons / actions will fix.
A compromise could be to add long-press actions to both variants.
Normal lyrics button long-press → toggle cover/lyrics
Toggle cover/lyrics button long-press → enter lyrics mode
That way users could decide which they prefer as the default option (single-press for toggle or to enter the full mode) while not needing to have 2 identical looking lyrics buttons in their interface.
You could add a note in the settings to make this functionality more discoverable but I don’t think there’s harm even if users don’t know it’s there.
There’s no reasons someone would need and use both.