You want a focus mode plugin:

https://github.com/ryanpcmcquen/obsidian-focus-mode

This is what differentiates Obsidian from many other note taking apps. Anyone who has an itch can build a plugin and customize it.

Unlike a venture-funded SaaS application there's no meaningful commercial incentive or issue with building something that will eventually get sherlock'd b the application vendor in the future.

Notion should enter "keyboard mode" as you start to type and fade out the header bar. You'll still need to close the sidebar since it's quite busy and we don't fade it automatically since it has an explicit toggle. I guess if you're building your own there's still too much noise. Good luck!

Yeah, that's a nice touch. Though the reading experience is also important. Notion is obviously super powerful and a more cluttered UI is hence probably unavoidable.

In Obsidian you can disable almost all of the UI very easily in settings.

Only the Hider plugin did 'most' of the job. But yeah, Obsidian is good with this (with plugins)

Are you talking about the sidebar? or is there some other element you'd like to disappear?

Oh, I like the minimalism of your start page, before you scroll.