On Canon EOS cameras, error 20 generally points to a mechanical fault, most commonly in the shutter or mirror assembly. Based on the symptoms you describe—especially no shutter movement after basic troubleshooting—service is the most likely fix.

One thing that has helped some users is a full power reset: remove the battery, turn the camera switch to ON with no battery installed, and leave it that way for an extended period (for example, many hours) before reinstalling the battery. If the camera starts working again, that suggests an electronic lockup, but if the error returns, there is still an underlying fault.

Since you’ve already tried the usual user steps, a recurring or persistent error 20 should be treated as a repair issue rather than a settings or card problem.