how does the save post button work?

I don't think it works yet

Sadly it doesn't work, dev is looking to fix it in upcoming updates though.

On wefwef nothing seems to happen. No color change and there's no saved button on the bottom toolbar

I haven't tested it on the desktop site, but it works fine in the Jerboa app. When you tap save, the bookmark icon turns white, and the post will be available from the Saved menu in the bottom toolbar.

Are you using firefox too?