commandCameraMode commands are missing in Carpet version 1.4.20 for Minecraft 1.16.4

No, it's not absent, it was removed on purpose, in favour of the F3+F4 vanilla gamemode switcher.

Since survival servers/worlds don't have access to that, at the same time an official Scarpet app that provides even better functionalities was released. You can add it to your Carpet to add the behaviour back.

See instructions on how to add it and its new features in its wiki page.

^