Dang, that sucks. Saving stuff on web versions is bit problematic. I tried to save those to browser local storage now. Usually I've used Unity's PlayerPrefs which saves to indexed db on the browser instead but that remains only for some specific url path and that changes when updating the game. So that's not great either. No idea why your local storage would have been wiped though... 🤔🤷♀️
So the downloadable versions are the best bet of course for having a proper save.
Yea I have given it some thought but not sure if it'd be worth it as the game is pretty niche. The browser version already should be kinda playable on mobile too even though there are some issues that'd need to be solved like all the tooltips. And iOS browsers and Unity web exports right now have some weird issue where UI keeps sometimes flickering. But that's out of my hands and will hopefully fix itself on next iOS update just like it suddenly appeared on 15 I think.