The maglev is Shanghai is super smooth.
TGV in France is super smooth. Maybe not quite as smooth but still smooth enough that you can have a tall bottle or glass on a table without fear it’ll fall over.
Then you’ve got a couple of places in Europe that hits 300 km/h, or near enough: Köln-Frankfurt and parts of the München-Berlin in Germany, Barcelona-Madrid and the Eurostar. All of these are super smooth.
The rest is just “high speed” marketing, sometimes done on tilting trains that’ll hit 250 km/h. The ones I’ve tried are not super smooth. Parts of the “higher speed” tilting trains in the U.K. are downright uncomfortable and can leave you travel sick at times.