Plausible.io generates a random string of letters and numbers that is used to calculate unique visitors on a website and resets this string once per day. All the data is isolated to a single day only. There is no way to know whether a person comes back to a site on another day. There is no way to get any kind of personal data from Plausible Analytics, and it does not track individual people. All the data is in aggregate only.
Plausible.io minimises any data collection in general and whatever it does track is kept fully secured, encrypted and hosted on a server in the European Union to ensure it is being covered by the strict laws on data privacy.
See Plausible.io’s data policy for the full list of data it does collect to display your web stats and which metrics it uses the data for.