It’s about power cords not properly installed electrical wiring.
Google for “power cords in walls” for tons of discussion about why not, and for national electrical code section 400.8 for the actual regulations. Probably US-centric but the general concerns apply.
If hiding TV power and video cables behind a few feet of walls is a code violating disease, the US has an out of control epidemic!
Note the practical difference between running fat insulated cables (so safe they are built to live bare in living spaces, often piled in knots behind furniture), from infrastructure wiring meant to be inaccessibly buried in home structures.
You may be right that technically it’s against code to tidily hide HDMI, USB-C or consumer power cables this way, but apparently there is no county in the US where city inspectors have been so unwise as to commit career seppuku for speaking up on that one!
It is not against code to hide low voltage signal cables behind the wall. It's only against code for mains voltage. And there are good reasons for it. Just because you showed up to this conversation not knowing what they are doesn't mean they don't exist.
Google for “power cords in walls” for tons of discussion about why not, and for national electrical code section 400.8 for the actual regulations. Probably US-centric but the general concerns apply.