There were multiple court cases and this practice was found unlawful (and actually against EU law). But the government did not issue automatic refunds, and instead requested that people "actively appeal" with some time limits. They also refused to pay interest on the money withheld.
AFAIK, only about 50M Euro was paid back. A lot of funds gathered between 2002–2005 was never returned.
I've been living in Finland for 10+ years, and this whole story was super surprising for me to learn because the prevailing notion among people here is that Finland is the land of law, and everything is done correctly and legally, always, and we can and should trust the authorities.
There was no VAT payable on the car tax of imported cars, only the ELV (ei-arvonlisävero, literally "not value added tax").
The ELV idea was that for locally bought new cars you did have to pay VAT on car tax, but for used EU imports that was not legally possible (cannot charge VAT again when importing used item from another EU country), so an equivalent non-VAT tax was invented so the full tax (inc. VAT/ELV) stays the same.
But this was unfair for e.g. the reason that Finnish companies buying cars could deduct Finnish car tax VAT on local new cars on their VAT return but not the car tax ELV on imported used cars (since it was not VAT).
There are lots of small issues (libraries or headers not being found, wrong libraries or headers being found, build scripts trying to run the binaries they just built, wrong compiler being used, wrong flags being used, etc.) when trying to cross-compile arbitrary software.
All fixable (cross-compiling entire distributions is a thing), but a lot of work and an extra maintenance burden.