Electrical shutters crash computer connected to same power line
At first I thought it was a cheap PC supply, but it's the stereo also.  This is big enough to affect both. 

It's voltage surges

When the curtain motor reaches position, it is disconnected abruptly.  The motor is an inductor. 

You may know a capacitor wants to keep voltage the same and will flow unlimited amounts of currrent in that effort. An inductor is the converse.  It wants to keep current the same, and will flow unlimited voltage in that effort. 

Interrupt a motor, the field current will want to keep going, and will spike voltage into thousands of volts.  

This is the bane of hobbyists trying to control motors, as they usually fail to account for the voltages into the thousands of volts that can result. 

It should, in theory, be inducting this onto the hot or neutral wire.  In fact, if the switch was interrupting the hot wire, I would expect it to not happen; however Europeans are super slack about hot vs neutral (their plugs flip over, even)... So the people installing them may have inadvertently wired them to switch neutral.  You could check that; it's an easy fix if it's wrong. 

Fixing it

How to hack the motors to not do that is a question for electronics.se. (in DC you'd use a freewheeling diode, but that's a nonstarter in AC; but mayve some sort of VBO device in the right place to act like that.) 

I have a feeling the curtains might've been built with such protection, but it has degraded, as MOVs will do.  Fixing that is not hacking, it's repair. 

To stay in our bailiwick, what you need is a commercial quality surge suppressor.  The consumer jobs won't cut it; they use cheap MOVs which degrade via usage, i.e. become "used up". And this setup would "use them up" quickly.  Meanwhile in America... NEC 2020 just made whole-house surge suppressors mandatory, so massive economies of scale are hitting the quality surge suppressor game.  That's what I'd get; a whole-house surge suppressor, and stick it right on that branch circuit between the blinds and the PC/stereo. 

Why is it affecting the ground wire?  Ground faults.  Consumer products typically have 500 or 1000 volt insulation between hot/neutral and ground.  Well, this interrupt voltage is so high that it's leaping not only over the insulation on the blind motors themselves, but on the stereo's as well.