Shipping is quite easy, especially for small and expensive things like laptops, where adding cost of DHL/DPD shipping is not a major deal.
Tangentially, as they are doing it already, selling _to consumers_ is quite hard. Each country has different regulation placing a lot of obligations on the seller.
From Poland: obligatory non-renunciable 24-month warranty of fitness for the intended purpose for consumers. Instructions required in Polish. Detailed information about qualities of goods sold is compulsory (e.g. specification of components for a computer, just model number is not enough).
From Germany: specific requirements for "impressum" on each website. Definition of all quantities in SI units.
Things get more funny if you touch any food: labelling regulations have a common EU base, but definition of what detail level is required for each element is per country, and they do differ significantly.
For everywhere: obligation to collect and report VAT for each destination country.
I'm a 1000% sure the place I order my stuff from in Germany doesn't have a representative in Finland.
That's the whole damn point of the EU.
I think there might be some regulation on having the instructions written in the native language, but that's like 100€ to a translator for an one-time job. No laptop comes with an extensive manual.
Warranty terms are EU-wide too mostly, there are some country-specific exceptions, but nothing that would require a huge legal team to handle.
Tangentially, as they are doing it already, selling _to consumers_ is quite hard. Each country has different regulation placing a lot of obligations on the seller.