Thunderbird configuration database as the settings for icloud. https://autoconfig.thunderbird.net/v1.1/icloud.com

So you will need to be more specific as to what your issue is as those settings are known to work and are based on this apple support document https://support.apple.com/en-us/102525

The Authentication method will be normal password, so I really do not understand your reference to google issues where the authentication method is oauth.

I have added Gmail and another account successfully to Thunderbird, but when attempting to add Icloud Mail it fails and says to check passwords, etc. Using the same credentials I can log into the icloud website successfully, so it is not my userid or password. I tried the method discussed here for the gmail issues but that made no difference. Adding Icloud mail is the last account I need. Any ideas or anyone else with same issue? Platform is Linux.

Yeah, iCloud won’t work with just your regular password, you need to generate an app-specific password from your Apple ID account settings. Once you use that in Thunderbird, it should work fine. Apple’s a bit picky with third-party apps like that.

You can create that app-specific password at account.apple.com.