First of all TÜV isn't a single org but a shared brand of multiple independent companies. And while "TÜV" is used colloquially for the mandatory car inspection in germany even all TÜV named companies together aren't anywhere near a monopoly: all of them combined(!) have 37,5% market share in the german vehicle inspection market. The largest single org in that market is actually DEKRA with 32,5%.

People say "Ich bring mein Auto zum TÜV", but they actually mean "I'm gonna drop it at my dealership and let him inspect it by whatever company he has a deal with"

src: https://www.kba.de/DE/Statistik/Fahrzeuge/Fahrzeuguntersuchu...