For whatever reason, the industry term for the certification is "Homologation" (1)

But yes, the vehicles which aren't on sale typically haven't been homologated. Why invest the time and money in that when it's not needed?

Actually deemed unsafe and not meeting the rules is much rarer, e.g. Tesla CyberTruck in Europe. (2)

In either case, you may get away with owning it, but not driving it on public roads.

1) https://en.wikipedia.org/wiki/Homologation https://www.productipedia.com/kb/productipedia/compliance-re...

2) https://www.theguardian.com/technology/2024/oct/08/tesla-cyb...