In article , Carlos E.R.
wrote:

I never understood well why a digital camera needed a mechanical mirror.

the same reason film cameras did, so that the viewfinder has an optical
path through the lens.

while digital viewfinders are much better than they used to be, they
are still not as good as a ttl optical viewfinder, particularly with
sports and low light. there is also no battery drain with an optical
viewfinder and focusing is faster.

And shooting slower. The mirror has to be moved, takes time.

so does flushing the sensor prior to the photo and then tripping the
shutter, usually using a mechanical shutter. electronic shutters may
work in some cases but can have all sorts of problems in others.

pro sports photographers, who can use whatever camera they want, choose
slrs because it's faster than mirrorless.

https://www.adorama.com/alc/wp-conte...utterstock_152
803373-2.jpg
https://fotoblog.hu/wp-content/uploads/2016/08/587168650.jpg

nothing is perfect in every situation.