Where can I find my Apple ID?

Typically an Apple ID is an email address you have used. If you are currently using a mobile device that is logged into your account, go to Settings and tap your name at the top.

Look in Keychain, and in a browser's security settings if you use it to automatically sign into Apple when using a browser.

This support article describes ways to find your Apple ID --> If you forgot your Apple Account primary email address or phone number - Apple Support

or go directly to this link --> https://iforgot.apple.com/appleid

If you find you can’t sign in, you can request account recovery (read this support article: How to use account recovery when you can’t reset your Apple Account password - Apple Support ) to regain access to your account. Account recovery might take a few days or longer, depending on the specific account information you can provide to verify your identity. More detail in —> Activation Lockout Issues - Apple Community

If you still need help:

Contact Apple for help with Apple ID account security "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues."

Contact Apple Support - Apple Support

If the OP did not have access to an Apple Account, they could not have signed in to this forum to post this question.

Safari may offer to let you sign in to the forums using Face ID, Touch ID, a phone's passcode, or a Mac's password. But when it does that, that's because the device is already associated with an Apple Account – an account whose Apple ID is displayed in Settings.

That's assuming they are using the same account to post here, or are paying attention during the sign-in process.