What does the pictured iOS Music app button do? Sometimes it's a red checkmark, other times it's a red down arrow.

What does the button do at the upper right (circled in green)? "Show Apple Music" is turned off in iOS preferences. I don't want to click that button, in case doing so causes the Music app to attempt syncing with Apple Music streaming, Apple Match or something equally destructive to my hand-curated library. I already searched discussions for 'checkmark', 'down arrow', 'red check' and 'red down arrow'--all lead me to MacOS Music app symbols/ download symbols/ wrong symbols associated with Apple Music. I do not have an Apple Music streaming subscription, nor do I pay for Apple Match; I only have locally saved music files, essentially using the Music app as iTunes/ an iPod. Thanks!