I nearly quit Medium after my first article was subjected to PWA - I think it's worse than Grammarly. It took me 2 months to have the guts to publish an article about the experience, which had been languishing in my drafts. One mention from someone who said they hated Grammarly, gave me confidence to publish. It was well received by some, but came with a backlash, which I wouldn't wish to repeat. https://medium.com/writers-blokke/when-illumination-said-my-work-had-83-errors-e5e2d152d305

By the way, if you go into edit, you can see the revision history, and revert to an earlier version if you like - esp if an editor has made unacceptable changes to your work. I didn't know this at the time.

The US English thing is a bugbear, but last time I asked someone not to change it in a private note, they didn't publish, so I'm wary. Some of mine end up a mix of both, which is actually worse.