Even at the time of its death, crossplay, cross save etc. didn't work except for a tiny handful of games. The Stadia Plus Chrome extension made a bunch of improvements on their own. There was never a desktop app. No ultra wide support. No RTX. Never got vsync working right.
In the years it was alive, what did they add? How come GeForce Now saw such activity and Stadia got... nothing? I wouldn't blame the people working on it, but some manager in Google really screwed that up.