MAIL IN FOLDER

Please re-state your question. I do not understand.

If your question is really about Thunderbird Mobile, you'd be best off asking it in that product's forum:

https://support.mozilla.org/en-US/questions/thunderbird-android

For Desktop, I do have Folder Oversea > Subfolder A ~ Z. so any email from A will auto go into subfolder A. But on my mobile, the email A will not appear on the mobile

Desktop Server: Imap Mobile Server: Imap Version for Desktop: 140.12.0esr (64-bit)

Your wording is vague, but it appears to me that your question has to do with some unnamed mobile phone email app. That would be beyond the scope of this forum, which is specifically about Thunderbird Mail for desktop operating systems. I recommend you contact the developer of the phone app..

I rephrase my question

My desktop do have Folder, so mail come in will go into individual folder.

As for my mobile app, there no folder in it. Those mail that fall into the Folder, sometime will not appear in my mobile app inbox.

See if you can subscribe to the folders on your phone. If you don't know how to do that, ask wherever support is provided for your phone app.

I get that. But please understand - your problem is with the phone app, not with Thunderbird. You won't even tell us what the phone app is or its operating system, even after you have been specifically asked. We couldn't possibly support other company's programs here. There's not enough volunteer expertise to do that. You really need to contact the phone app's tech support or help forum.