Test and trace never worked nearly as effectively against Covid as the media claimed. I don't know about the Netherlands, but here in the UK the media coverage was pretty much outright lying about how well it worked in South Korea to convince us our government was incompetent and had failed, saying it let them achieve things like lifting social distancing restrictions and reopening bars and clubs pre-vaccine when in reality every time they tried that cases immediately went exponential and they had to reimpose the restrictions. Even the countries which were pursuing zero covid with some success had to rely on repeated, strict lockdowns to achieve that (and most of them have given up on that now).

And it's been much more effective pretty much everywhere at preventing Covid getting in than it has once it's endemic in a country - reducing the number of cases doesn't help much if there are undetected infections, and the difficulty of finding those doesn't really scale down much with the number of cases or infections since they could be almost anywhere in the population.