I got introduced to microcontrollers through the original Arduino board. It took me only a year to switch to bare metal atmega/attiny (zero external components!), and to this day, those are my favourite micros despite all their shortcomings. Theyare extremely well documented, and them being 8-bit with a simple instruction set makes it very easy to learn assembly (or even opcodes). At the same time, they are compatible with 5V logic (and can be abused!) which makes them almost perfect for beginners.

Would I have been able to learn assembly with ESP32? Probably not. You couldn't even find proper manuals for ESP8266 back in the day because they either didn't exist, weren't in English or weren't released to the general public...