If you could get a power supply that could supply 220V DC and you put 100 of these LEDs in series with 220 ohm resistor
I would like to set in series 4 LEDS to blink when called upon, and hope I can get away with a single resistor..Can I?
Is that youtuber full of crap
there is no reason they wouldn't work because you have not violated any rules. I wouldn't do this if I were you because 220V dc is lethal and could kill you.