uPlot requires a csv-like data structure as seen at the top of https://jsfiddle.net/v439aL1k/

feel free to experiment, but i suspect that any workable solution is not going to be cheap enough and is likely to not be simple and high quality.

you must be able to simplify each data series as a stream (during the path drawing loop itself) rather than allocating another set of 3 x 50,000-element pixel offset arrays, which will eat up all the benefit very quickly.