Question about Bosch Home & Garden AdvancedVac 18V-8

You can do this in principle, it also works for water, etc. I wouldn't do it for fine construction dust. It doesn't do anything to the unit, but yep, it can sometimes blow something out the back again.
So as a tip. Especially if you have vacuumed without a bag and want to blow something up afterwards, I would first pre-clean the hoover and the hose in the open air, as in blowing it out 😉 The hoover can be cleaned with a hoover.

Yes, it can. I have always used it without a bag. It is designed for that.