SENDFILE_MODE missing from Settings

It might be hidden yes, in 99% cases it should stay that way with the default setting.

Switching it to xmds downloads, will only make it slower and much less reliable, but if you do want to try it, then you sure can.

It will involve database access, please see - How can I run a SQL command when using a Docker Install?

Then you can run the command like this:

UPDATE `setting` SET `value`='Off' WHERE `setting` = "SENDFILE_MODE";

Alternatively you can run (to see the settings in CMS Settings in web ui):

UPDATE `setting` SET `userSee`= 1 WHERE `setting` = "SENDFILE_MODE";

and this one to be able to change the mode in CMS Settings page.

UPDATE `setting` SET `userChange`= 1 WHERE `setting` = "SENDFILE_MODE";