Is thunderbird Running of the i-Pad?

No, no support for Apple mobile devices yet, just for most desktop operating systems and Android. The most recent progress report I know of is this, which is more than a year old now. It was then, and appears to still be in early development: https://blog.thunderbird.net/2025/05/thunderbird-for-mobile-april-2025-progress-report/ If you go to Github, you can see that the project is very active: https://github.com/thunderbird/thunderbird-ios