The SET command is specific to versions of OS/8. Can you paste in the start-up message you get that gives the OS/8 version?
For example, this shows I'm running OS/8 V3D with V3Q of the keyboard monitor and V1F of CCL. As you see SET TTY SCOPE and SET TTY NOSCOPE works. I'm surprised that "NOSCOPE" and "NO SCOPE" made no complaints.
wdc-home-3:trunk wdc$ make run
PDP-8 simulator V4.0-0 Current git commit id: ab48f313
Loading OS/8 from the RK05 cartridge disk in the build directory...
PiDP-8/I trunk:id[ef267a71d2] - OS/8 V3D - KBM V3Q - CCL V1F
Configured by w...@wdc-home-3.lan on 2022.01.01 at 16:21:48 EST
Restart address = 07600
.DIR - to get a list of files on DSK:
.DIR SYS: - to get a list of files on SYS:
.R PROGNAME - to run a system program
.HELP FILENAME - to type a help file
.SET TTY SCOPE
.SET TTY NOSCOPE
.SET TTY NO SCOPE
.SET DEV PARAMETER(S)
.SET DEV NO PARAMETER(S)
READONLY DECLARE DEVICE TO BE READ ONLY
FILES DECLARE DEVICE TO BE FILE STRUCTURED
FLAG IN TTY FLAG LOWER CASE CHARACTERS
SCOPE ERASE CHARACTER ON TTY RUBOUTS
ESC PRINT ESC(ASCII 033) WITHOUT CONVERTING IT TO $ SIGN