The difficulty is still the same: for each piece of the puzzle (substations, high voltage power lines, transformers, generators, loads), they have to wait until enough power is available at the connection point, and carefully manage the power balance so it's neither too much nor too little (and if they get it wrong, things trip offline and they have to start all over), while the grid is in a degraded state (often meaning no alternative paths, so a single fault can set them back several steps). The only difference being that the black start "generators" are these still working international links (which could be very far from the important parts of the national grid).

It might be faster to instead black start several independent power islands in parallel, and connect them together as a final step. At least in my country (Brazil), that's how it's done for large-scale blackouts, even when some of the country still has power; it was done that way for the partial blackout in 2023, and there's a written procedure on how to do it (which is available on the operator website, if you know where to look). In 2023, some areas failed to black start for one reason or another, and had to wait for power from the outside; other areas managed to black start as expected, and were then synchronized with other areas until everything came back together.

The grid is not just an aggregation of individual sources and sinks; it takes active effort to keep them all working together in a useful way without just collapsing again into another cascading failure. For that reason, your solar inverter doesn't come on until the grid operator wants the solar inverters to come on in your section of the grid.

It's tempting to think of the grid as something grid operators control, feeding power from point A to point B, but the grid is actually largely uncontrolled - the power just flows wherever it wants to - and the only controls they have are turning on and off generators, adjusting their throttle, disconnecting loads (rolling blackouts) and sometimes opening circuit breakers (though this is not normally useful). They don't even have precise real-time monitoring of the whole grid - only specific measurements in specific locations, from which the rest is estimated using lots of maths (which is how you would design it too, if measurement devices cost $100,000 apiece). That's why it's not a trivial task to keep it working.

However, you're able to have your own, private miniature grid, on which you can power your own loads from your own generators. It's even possible to do this with solar inverters! You will need to specifically seek out this capability, and get extra hardware installed, which is probably why you don't have it. You need a "transfer switch" to definitively disconnect your private grid from the main grid when you're using your private grid capability - it's not allowed (and not safe, and will blow up your equipment anyway if you force it) to just feed power onto your local unpowered section of the grid.

As in the German government and most of the political class...