Automatic lights can mainly adjust the focus angle of light according to the zoom of the lens, and can "automatically" determine the intensity of flash. The whole process is very complicated to do a good job of flash intensity. Usually, a series of lights with different intensities will be emitted quickly before the official flash, and then the lighting conditions will be measured every time, and then the final flash intensity will be determined through complex calculations.
The lighting situation at the wedding scene is more complicated, it is difficult to get it without automatic lights, and many shooting opportunities will be missed.
I used Nissin's automatic lamp Di622 on Nikon's machine before, and the price of this lamp is 1000 yuan. But it's embarrassing. It's not bad to jump and flash, but it's always black when it flashes. However, flat flash generally can't produce good results, and I'm too lazy to talk to manufacturers. Wedding photos are enough.
Now there is a Sony micro-single. Some time ago, I put a Yongnuo manual light, which was less than 300. In fact, manual adjustment is just as easy to use. Just not as fast as automatic, hehe.
In addition, don't think that the effect of automatic lights will satisfy you. ISO setting and shutter speed setting are exquisite. What you said about "what mode of SLR can automatically change the light into the corresponding mode" is too general.