It usually depends on which switches and motors you use in the end. Some manufacturers have special features and yes, everything also works without bus systems.
So that would mean I install a timer switch on the ground floor and upper floor. These then switch the respective switches on the windows OPEN and CLOSE with a closing contact, blinds operate. And from the switches, the OPEN and CLOSE contact goes again to the corresponding blind, which I can thus operate individually; additionally, an isolation relay must be built into the switch?
As mentioned, there are different possibilities and systems, but yes, as you describe it, it can be done. In addition to GIRA, other manufacturers also offer ready-made switches with auxiliary inputs, that is, ones that can be operated by another.
It would of course be easier, for example, with Homematic Ip. You don't have to do any special wiring, just install a switch on each roller shutter (which is not mandatory) and then you have a central station that is radio-controlled. You can then pair additional switches or remote controls, smartphones, and all kinds of automation with it.