I think starting and investing per-se really isn't the major issue for some time (at least in Sweden and probably Denmark), we've gotten many small business friendly laws over the past 15-20 years.

At the same time there are many discrepancies that makes it hard for companies from one country to mesh with companies from another country.

Law tradition (Napoleonic, German or Nordic), tax rules (German rules were (are?) notorious for their complexity,etc. , then there's certain laws such as the Finnish money gathering law that can be a problem for very early stage development ( https://solhsa.com/wishlist.html ).

All the above creates friction, and if EU-inc would follow German rules, I'd rather just stay with a Swedish company because..

Luckily the EU has harmonized things so a startup in one country can mostly work within local rules as long as we make sure to distribute earnings from different countries correctly.

The trickier part is forming bonds, such as for investor and/or startup protection for across-border investments when one wants to grow, various scams over the years has played out differently in various countries so those kinds of laws could be quite an issue outside of the stock market.