FYI this is from 2022 but is relevant because Thunderbird (and K9 v8) just landed in F-Droid (and other android package managers I guess but I haven’t checked).
The process of importing from K9 Mail worked without issue for me. There is also the option to import from desktop using a QR scanner (or some kind of scanner, again I didn’t go down that rabbit hole).
FYI this is from 2022 but is relevant because Thunderbird (and K9 v8) just landed in F-Droid (and other android package managers I guess but I haven’t checked).
The process of importing from K9 Mail worked without issue for me. There is also the option to import from desktop using a QR scanner (or some kind of scanner, again I didn’t go down that rabbit hole).