Title says it all. Currently I have a Conon EOS R50 with a Canon RF-S 18-45mm f/4.5-6.3 IS STM lens. What is the best way to take full power arc shots with this setup? How do I remove flicker?

Get yourself a ND1000 filter and use manual mode or aperture mode with exposure compensation to adjust optimal exposure and depth of field. Technically, Hoya makes good ND filters, but also cheap Chinese ones are also adequate for this purpose. A lens with good macro capabilities is required, too. Experiment with exposure times resulting, often short exposures, shorter than a line half-period, can catch interesting dynamic colorful effects in the discharge. Shooting the lamp right after ignition can also reveal something cool looking.