Da Flex sorry, but Zygmunt is correct here. With an underspecced cable you'll get signal drop outs (down to no signal at all) but you should see 4kp60 listed in settings.
Missing modes is usually caused by software/EDID issues, i.e. the AVR or TV isn't advertising the correct modes or the RPi4 hasn't been configured to 4kp60 in config.txt and thus won't use the mode, even if the TV/AVR advertises that capability.
so long,
Hias