> The Local Folders Account has a setting to set the Message Store Type. By default it's set to "File per folder (mbox)". How can I switch to Maildir?

Just change the selection.

> Note that in global Settings, I have already set up the Message Store Type for New accounts to "File per message (maildir)". But I can't create a new local folder account.

There is not a global setting for store type - it is strictly per account. Multiple local accounts is not possible through the UI.

> There is not a global setting for store type - it is strictly per account.

Correction, there is a global value, but that changes the default for NEW accounts. It does not affect existing accounts.

> The Local Folders Account has a setting to set the Message Store Type. By default it's set to "File per folder (mbox)". How can I switch to Maildir? Just change the selection.

I can't change it. This setting is locked. Probably because of the above (we can only change this for new accounts).

> There is not a global setting for store type - it is strictly per account. Correction, there is a global value, but that changes the default for NEW accounts. It does not affect existing accounts.

I agree with this. How can I make the "Local Folders" use the new Message store type configured (i.e. Maildir)? I assume I'd need to remove the local account first and create a new one. However, I can't do any of that. I can't create a new local accounts either.

Additional Local Folders can be created in TB 128 with an add-on, but I don't know if new locations will apply the maildir setting.

https://addons.thunderbird.net/en-us/thunderbird/addon/localfolder/

Additional Local Folders can be created in TB 128 with an add-on, but I don't know if new locations will apply the maildir setting. https://addons.thunderbird.net/en-us/thunderbird/addon/localfolder/

Thanks for sharing. The add-on does not have support for the latest Thunderbird version (140.0), which is the one I'm using, so I can't try if that plugin would work.