I think you might both be right- the author may be thinking of lower cost MCUs only aiming for tolerable ADC performance, while you might be thinking of all MCUs, even higher cost.
The RP2350 has 9.2 ENOB on a 12 bit ADC. Sure, you might be able to decimate multiple samples to get more bits out of them, but the spec sheet supports the author's claim (https://www.raspberrypi.com/documentation/pico-sdk/hardware....). There are even lower cost MCUs like the CH32V003 that have even worse ADC performance.
On the other hand, some MCUs can definitely do 10+ bits, such as the STM32H7 line which gets 13+ ENOB from a 16 bit ADC. This is impressive, but the H7 MCUs are literally an order of magnitude more expensive than the RP2350, so they might not be something the author tinkers with much.
https://www.st.com/resource/en/application_note/dm00628458-g...
The RP2350 has 9.2 ENOB on a 12 bit ADC. Sure, you might be able to decimate multiple samples to get more bits out of them, but the spec sheet supports the author's claim (https://www.raspberrypi.com/documentation/pico-sdk/hardware....). There are even lower cost MCUs like the CH32V003 that have even worse ADC performance.
On the other hand, some MCUs can definitely do 10+ bits, such as the STM32H7 line which gets 13+ ENOB from a 16 bit ADC. This is impressive, but the H7 MCUs are literally an order of magnitude more expensive than the RP2350, so they might not be something the author tinkers with much. https://www.st.com/resource/en/application_note/dm00628458-g...