In case I was unclear, I only enabled developer options and made any changes in settings AFTER I was having this issue, which has been ongoing since the very start of installing GrapheneOS. The issue was not present before installing Graphene OS.
This does not mean it's not a configuration issue with your device.
This is clearly an issue with the operating system. My friend has also been trying GrapheneOS for the first time and has been experiencing similar issues, such as Teams and other apps not functioning in the background and completely missing work notifications.
They do not have their device configured correctly. Teams depends on Firebase Cloud Messaging for push notifications which means sandboxed Google Play needs to be correctly installed and configured. It's not intended to function out-of-the-box and ignoring the prompt about the battery optimization exception will cause this, as will having data saver or battery saver enabled.