There was Nokia's MeeGo that failed in 2011 despite being far more polished. Even then iOS and Android were already too established.

You're posting on a discussion board about the tech business. Surely you must understand what network effects are.

Like what? Blackberry OS and Windows Phone are dead. There aren't any feasible smartphone platforms out there besides iOS and Android, unless you think your average consumer should be buying a Pinephone or something (and I wouldn't consider that anywhere close to feasible anyways).