T-MST10DEUC-1034.1, BT-G
Was rooted a while ago (software update disabled with methods listed on this site... a year go).
Then "something happened", widgets gone, root gone. (well, can't FTP or telnet to it).
Tried resetting smart hub, widgets gone, still can't login as dev, or open anything.
Tried method in OP (created InstallSamygo/data on a FAT32 USB, put 128.xfs file into it, plugged it into TV, switched it on).
I don't see "install widget" option in smart hub.
Any clues?

Standard Samsung stuff doesn't work either. Trying to login asks to "wait" (I recal one needed to create "some" account, to create dev account), trying "social" button gives black screen.