Here’s another thread from a year ago: [Bug] Absurd route time estimates
I hope this one does not end with the usual sequence of “There’s no issue”->“We have more important features to work on”*->“Edit OSM yourself to add speed limits and thus work around the bug in Kurviger”
(* - IMO you have nothing more important left to work on than reliable ETA, which is the second most important feature of any nav app.)
Meanwhile, on the same routes, your direct competitor Calimoto had that issue solved since at least 2020, giving very accurate estimates, with Google Maps and Waze not far behind. So the problem is not the lack of data in OSM, but particularly faulty way route time estimation works in Kurviger.