Depends on the aircraft. Some modern jetliners are using fly-by-wire, while others have hydraulically-boosted controls. Some still rely on cable-and-pulley.
Either way, as I understand, it wouldn't matter with the MCAS-related MAX aircraft crashes. The elevator trim is able to move the entire elevator (literally, the entire elevator moves in response to the jackscrew controlled by the trim system) to such an extent that, depending on CG, airspeed, and other factors, it cannot be overpowered by moving the control surface to its full deflection. So whether or not the MAX had boosted controls or fly-by-wire probably wouldn't have mattered in the case the aircraft were trimmed fully nose-down. The pilots would have been struggling to maintain control either way. That's why there's stabilizer trim cut-out switches and manual trim.
I'd highly recommend Mentour Pilot's videos on the subject, links below:
Either way, as I understand, it wouldn't matter with the MCAS-related MAX aircraft crashes. The elevator trim is able to move the entire elevator (literally, the entire elevator moves in response to the jackscrew controlled by the trim system) to such an extent that, depending on CG, airspeed, and other factors, it cannot be overpowered by moving the control surface to its full deflection. So whether or not the MAX had boosted controls or fly-by-wire probably wouldn't have mattered in the case the aircraft were trimmed fully nose-down. The pilots would have been struggling to maintain control either way. That's why there's stabilizer trim cut-out switches and manual trim.
I'd highly recommend Mentour Pilot's videos on the subject, links below:
Runaway Stabilizer: How to stop MCAS - https://www.youtube.com/watch?v=xixM_cwSLcQ
Boeing 737 Unable to Trim! Cockpit video (full flight sim) - https://www.youtube.com/watch?v=aoNOVlxJmow
Five questions about the Boeing 737 MAX Answered - https://www.youtube.com/watch?v=CD0JabYjF3A