More broadly, a genetic database needs to cover only 2% of the target population to provide a 3rd cousin match to nearly any person

https://www.science.org/cms/asset/089c0893-0dc3-4668-be4a-cff6d3915fad/pap.pdf

Since I don’t know about newer studies, I will correct myself to 2-5% to identify the rest.

My 1% came from a german source (Question at the Bundestag by Die Linke-party) which could still be correct though:

Currently, over 1 percent of the population in Germany is already registered in the DNA analysis file (DAD) of the Federal Criminal Police Office (BKA). This means that, statistically speaking, most residents have a third-degree relative in the database (see: ç). In other words, if familial searching were applied to the DAD, then theoretically, via the detour of near matches, every resident could be identified via DNA analysis, provided that sampling is uniform and unbiased

https://dserver.bundestag.de/btd/19/040/1904087.pdf