Is the photo taken by SLR in the studio very dark?

That's not black, it's gray. It's a good film with low light ratio.

Your lighting layout is not as low as the light ratio caused by the main light. Try to set the light output of one side to 50% of the main light source. If you can't adjust the light output, you can take off the soft cloth in front of the main light source and try to keep the auxiliary light source away from it. Try to adjust the incident angles of the main light source and the auxiliary light source.

See if your ISO and aperture are different. Is it better to use automatic gear or shutter? Don't use automatic gear or shutter priority. If you can't master it manually, you should also use the aperture first. The product film should be shot with small aperture and low ISO. These two items must be set manually. If you are afraid of slow shutter speed, put on a tripod, release the shutter with a cable or increase the output of the lamp.

The product film must be post-produced, and the post-production should use RAW files.