In general, read-out protection provides a very limited level of protection that I wouldn't rely on to stop cloning. There's quite a few firms that will extract the firmware from protected microcontrollers for a couple thousand dollars (i.e. https://russiansemiresearch.com/ ) which is a drop in the bucket considering the potential profit from industrialized cloning. Lots of microcontroller series also have exploits that can allow hobbyists with very little funding to bypass read-out protection (here's one for the STM32F0 series for example: https://github.com/racerxdl/stm32f0-pico-dump ).
Can you explain how? Genuinely curious. The author only refers to "security theater" which seems to be when a product or system around a product makes people feel like they're safer, when actually it's not making anything more safer or more secure.
I suspect this mostly refers to "Code Protect" or similar functions, that are designed to stop the user for extracting the firmware from a device in the field. Typically, when this is enabled, large parts of the debug interface stop working, and turning it off requires a "secure" erase, that clears the loaded firmware.
While many CP implementations are flawed, or can be bypassed by a skilled attacker (power glitching, &c), I wouldn't say they are purely theater, as they raise the required investment from a <$10 ISP to $$$+ for something like a chipwhisperer.
Even with chip security features this is still the case (if an attacker gets their hands on it it can be compromised). There's no chip that exists that I'm aware of that can't be compromised to have its firmware dumped.
It's like locks: Every time a manufacture claims to have made an unpickable lock someone goes and picks it. It's the same for chip security features.
Microcontroller "security" features really are security theater and not actual security. The only real reason they exist is because certain vendors/"big buyers" will require it as part of their parts checklists (which is silly) and it provides a way for chip manufacturers to wriggle more money out of each sale.