I've been experimenting with 4DOS and found that it supports LFN. This is convenient, except that it only seems to work with the much older STARLFN and not with DOSLFN, which is otherwise the most up-to-date software available for this, last updated April 2022.

The functionality is enabled automatically, so long as STARLFN is loaded. It can be seen by DIR producing two columns, with the long file names appearing on the far right side.

Does anyone know why 4DOS doesn't work with DOSLFN?

There also seems to be a problem with dates when using STARLFN with MS-DOS 7.1 COMMAND.COM. It does not appear to be an issue for 4DOS though. Very odd.

STARLFN can be found here:

https://sta.c64.org/starlfn.html
https://sta.c64.org/starlfn.zip

DOSLFN here:

http://adoxa.altervista.org/doslfn/
http://adoxa.altervista.org/doslfn/dl.php?f=doslfn

and 4DOS here:

https://4dos.info/v4dos.htm
https://4dos.info/4dvers/4dos800.zip