Siri doesn’t work with the latest iOS 14.5.1 update

Settings > General > Reset > Reset All Settings seemed to resolve the Siri not working problem for me. I've not yet tested to see if CarPlay is working again (and will probably have to set up CarPlay when next I get in the car). You end up having to re-set up a bunch of stuff, but it's not a full-blown Erase/Restore operation.

https://discussions.apple.com/thread/252767696?answerId=255212008022#255212008022

Greetings mattstanley892!

Looks like you are having some trouble with Siri not working after updating. We want to help! To start, do you have a stable internet connection when this issue is occurring? What happens specifically when Siri isn't working? Do you get any error messages or statements from Siri about what the issue is? Try restarting Siri by going to Settings > Siri & Search > "Hey Siri" off, then enable that setting once more and test again.

Have a great rest of your day!