Both AFFiNE and Joplin Notes are intended for creating and editing notes, with a view to building up your searchable personal knowledge base.
My video does an in-depth dive comparison between AFFiNE and Joplin Notes with a primary focus on the note-taking capabilities and their Markdown format compatibility. AFFiNE has the added advantage of providing some great graphical tools with its edgeless canvas mode, whilst Joplin Notes has tremendous extendability through its numerous community plugins.
They do things slightly differently and neither, though, does everything perfectly, so my video will hopefully highlight some of their differences which may appeal to you.