Can WordPress and Tumblr compete with Facebook?

No! I'm glad that WordPress purchased Tumblr which was for sale in a fire sale but they're not going be able to build a Facebook competitor. They will build a better CMS. It'll be fun to use, but not a Facebook.

Is Huawei's HarmonyOS an Android replacement?

It is not. It is a good start on an android replacement. To replace Android you would need all the app developers to join as well.

Is Twitter doing a good job at cleaning up its platform?

I hate to say this but it's not. They are trying. The changes they make are good changes. But Twitter fundamentally, right now, is making democracy worse. It's making conversations worse. It's stressing people out. It needs an overhaul. It needs bigger changes than what the company is doing right now.