Welcome back james.horak.
We apologize for the previous response as we meant to say Thunderbird for Windows and the Outlook app for Windows. In using those apps or webmail, you will need to use the app-specific password in order to get your iCloud emails using those third party apps. Please see the section titled “How to generate an app-specific password” in the previously provided link. Then, you will use your app-specific password with your iCloud email when setting up iCloud email with Thunderbird.
If you have further questions regarding your Thunderbird email, we recommend contacting them here: Thunderbird Help
Let us know if you have further questions.
Take care.