Doesn’t every country have an exit tax, tho? Some are worse, some are better, but this is always the case.

Lots of countries have some level of exit tax on unrealised capital gains, but the devil is in the details. A painful part in the German case is that they have a fixed company valuation method that might make it untenable to leave the country.

It's one thing to tax people on assets they actually have or that are easily realisable like ETFs, as they then pay a portion of money they have ready access to. It's quite a different thing to invent a value for something and tax on that. The company ownership in question might not be realisable at anything close to that amount, especially for a startup, if you don't leave before making a profit

So don't do startups in Germany. The exit tax is just one of many reasons for that, the whole German system is bureocratic and inflexible compared to nearby countries.

The EU forces every member state to implement an exit tax to trap entrepreneurs in a disadvantageous situation (Anti-Tax Avoidance Directive).

Some countries such as Sweden implements this only minimally - making capital gains of Swedish companies you hold realised within 10 years of moving abroad are taxed, so just don’t sell in 10 years but take out credit with those assets as collateral.

Of course outside the EU, such as Switzerland and the UK, these governments are not bound by EU rules and don’t impose exit taxes.

Which is why so many European millionaires are doing their best to live in these countries

The UK doesn’t.