WordPress.com is a desktop app that gives your blog a permanent home in your dock.
Features:
Focus on your content - Write and design with no other browser tabs to distract you. Switch easily between managing your WordPress sites and your favorite desktop apps.
Speed is a feature - The desktop app builds upon the already fast WordPress.com by bundling the entire site as a local copy. You get near-instant page-loads and less waiting around.
Not one size fits all - The WordPress.com desktop app will scale to any size. Do you need a small window on the side to keep your eye on notifications, or do want to expand to a truly full screen for a zen writing experience? Take your pick.
AFAIU the difference between wordpress.org and wordpress.com, the latter is a company making money out of a free product (the .org one). Using the same name is very confusing (and probably on purpose)... On the positive side, they offer hosting service for the basic plan, but many are cheaper. Hopefully, their support is worth those 50 bucks a year. ;-)
Reminder: Keep WordPress AND the plugins you use UP-TO-DATE! They are almost constantly being found to have security flaws. - - EXAMPLE: "Hackers are exploiting a critical flaw affecting >350,000 WordPress sites. Flaw is in *File Manager*, a plugin with more than 700,000 users; 52% are affected." - - https://arstechnica.com/information-technology/2020/09/hackers-are-exploiting-a-critical-flaw-affecting-350000-wordpress-sites/