DSLR has a shutter that covers the sensor. Mirrorless is always open. Wait.. wasn't there a firmware update from Sony that allow the shutter to close..?
Dsir don't have shutter close down when changing lens , only the reflex mirror in front of the sensor ..
but Canon eos R when changing lenses, a shutter close down so the sensor cover block the dust to go in .. our Sony don't have, easy to collect dust..