I tried to control WS2811 LED strip with 12 V power line.
After testing my ESP32 program I connect the strip with a ground and data cable. The power (12 V) was only connected to the strip.
My ESP32 immediately stopped working. It appeared that there was 12 V on the data line, which burnt ESP32.
The question is: is it expected to have 12 V on the data line?
No it is not expected. If you look at a typical datasheet for the chip itself the input levels are 0.3 and 0.7 times Vdd, which is maximum 5.5V (minimum 4.5V) and comes from an internal shunt regulator.
The maximum input current is also < 1uA so it is supposed to behave more-or-less like an open circuit for inputs between GND and Vdd.
So '0' is < 1.35V (4.5V Vdd) and '1' is > 3.85V, so it cannot necessarily be driven reliably directly by a 3.3V MCU.
If the ground was not properly connected to the strip then bad things(tm) could certainly happen because that would conduct current through the protection diodes in the chip.
