Yes. Follow Apples guideline and generate an app specific password and use it instead of your normal password. This is a Apple issue not a Thunderbird issue. https://support.apple.com/en-us/HT204397

I followed Apple's guidelines and the app-specific pwd generated was aloso not accepted

This Thunderbird user figured it out. Maybe it will help you. https://support.mozilla.org/en-US/questions/1026598

Or maybe this. https://www.lifewire.com/how-to-secure-icloud-mail-1172270

yes, I did all that but Thunderbird does not accept the app-specific generated pwd

Check your mail server settings using this Apple support page.

Also checked mail server settings...no idea what else to do

leonorbarroca said

yes, I did all that but Thunderbird does not accept the app-specific generated pwd

Thunderbird could care less what you use for a password. It is your providers sever that accepts or rejects it. Sounds like you need to contact Apple for help.

how to fix icloud with thunderbird. 2step authentication

https://support.mozilla.org/en-US/questions/1174729