What does the $50 get you with Obsidian? I don’t pay, and I’m able to access my notes from my desktop and mobile apps.

They must be talking about the commercial license.

[0] https://obsidian.md/pricing

Obsidian is free for individual use. The $50/yr is a commercial license. They also have a $4/month sync product (sync across devices with e2e encryption), but you can use icloud, google drive, etc too.