ENIAC might not even be considered a computer by our standards now. That device and possibly some of the others you mentioned did not store programs in memory. That detail would make it difficult to have program(s) that help someone manage the running of the machine. That is the essence of an operating system is a program or programs that help you manage the running of the machine.
ENIAC was programmed with patch cords, dials, and switches. Programming was very expensive, a program to help manage the running of the machine would have been considered too expensive, even if they had thought of it.
I think the Mark 1 was one of the earliest to store programs in memory. That innovation would have made writing programs to help manage the machine more practical. Even after it was possible, create these types of tools there was plenty of toggling machine code in manually.
Even as late as the 1970s I remember sitting in a computer lab toggling in a small machine language program into a PDP11 so it could read a paper tape that would load a programs that would let me edit, assemble, run, read, and punch assembly language programs.