Interestingly, Germany is also known for its unusual (within EU) acceptance of modified cars and high speeds...

Where else can you expect a heavily modded Volkswagen Golf from the 90's to overtake you at 220 km/h on your way to work?

Modifications are actually strictly controlled, compared to the US, also your vehicle has to pass a mandatory safety check every two years.

The high speeds are a point of controversy. The pro high speed people say we have a low death rate, the pro speed limit people say all the studies indicate it could be way lower with more sane limits.

Your example is actually somewhat common and it can be surprising how a car that isn't in view on your first mirror check can be next to you on your next mirror check, when you're driving 120kph.

The fact that your modifications are strictly controlled DOES cause a market demand, that drives innovation and high quality in the aftermarket parts industry. Especially when it comes to engine modifications where they must be emissions-compliant. We have a lot of these hard regulations to thank for the availability of good quality aftermarket parts (compared to say, the 1950's and 60's.)

This, however, comes with the drawback of a quite high price. And there are quite a few things you can do in the US which you may not do in Germany, for example under car lightning, additional front lighting (think the illuminated Mercedes logos), anything that negatively impacts the emission profile much and - my personal pain point - large wing spoilers.

I can see the reason for most of these - if you're allowed to go 300km/h in that car, it should definitely be in a good condition -, but it's not without drawbacks.

And then there are those who consider the high speeds a considerable safety win (because it greatly reduces inattentiveness for everybody involved), and only advocate for limits because of the massive energy demand of high speed.

Not Germany, thats for sure. Germany is regulated up the ass, TUV approved bumpers, lights, bike racks, tail pipes, gas caps, everything.

Just get a motorbike! Whenever I got stopped by the police and showed them my paperwork (i.e. a huge list of ABEs - like 10 or so), they just got annoyed and told me to just drive away already ;)

Half the stuff wasn't even approved for my bike, but no one ever checks if you just confidently hand over a small book worth of paperwork...

Yes, approvals are required, but this approval is straight up impossible in most EU countries.