The following instructions explain how to create a local folder in Thunderbird and back up your emails locally

1. Right-click on "Local folders" and select the "Settings" option

2. select "Local folders" in the account settings and select a folder (storage location) on the right-hand side

3. after confirming the path, Thunderbird must be restarted

4. the mails can now be copied into the newly created folder using "drag and drop" or "copy and paste"
5. you can now find the copied mails under the path specified above