Good afternoon GSR99,
Welcome to the Apple Support Communities!
It sounds like you are having trouble with Siri finding music from the Apple Music catalog since updating to iOS 14.5.1. We're happy to look into this with you.
Let's try turning off all of the Siri Music settings, restarting your iPhone, and then enabling them again.
Tap Settings > Siri & Search > Music to access these settings.
Is this happening when using a local Wi-Fi network, cellular network, or both?
Have you tried using a different network?
Are you able to search the Apple Music catalog within the Music app without using Siri?
Check the Apple System Status page to make sure there are no current issues with the Apple Music service.
Please reply to this thread when you get a chance so that we can determine if the issue is with Siri or the Apple Music service.
Take care.