The EU means it would be entirely legal and tariff-free for a company in France to ship a product to Spain as-is, with minimal caveats. But that won't be a desirable product for most Spanish customers.

The vast majority of that list has nothing to do with laws, but with physical requirements (keyboard and power plug), payments (not standardized beyond bank transfers), localization, and logistics.

I'd expect a cable C5 to Shucko to work everywhere in Europe (at worst you change the cable for preference to avoid an adapter)

And would not be acceptable in any other country than Germany legally. Got bitten by that while searching for industrial plug…

It's very much a work in progress, especially since overall progress is happening at the same time.

27 countries need to coordinate to first agree to grant the EU the power to take over some aspects and then those same 27 countries need to actually do the work, together with the EU, to standardize that aspect. Then the standard needs to be adopted and enforced.

The EU has less power than a confederation, which is a very weak supra-statal organization. So everything is very, very slow.

The EU is gradually able to do more and more, but the time frames are decades long.

That's mostly self imposed legal and paper work. They could ship the German version EU wide, but they don't. Because they want to "provide the best experience". You know what would be the best experience? Buying the damn thing without paying extra for mail forwarding.

It does help (for example the mentioned CE certification is EU-wide). But it definitely could be better. I'd suggest it's not likely to change significantly any time soon.