Adding custom block problems
There are two different "block things". Actually, three.


First, there are block plugins. That's code, that's what you have. It's the thing you select on the block layout page. It's not something that you can list with views (Well, theoretically, it would be possible, but you would have to write a views query plugin that queries plugins.)
Then, there block config entities. That's a plugin + configuration, a block placement.
Last, there are custom blocks or content blocks. Those are content entities, similar to nodes with different types, fields and so on. Those are the user-created data. Each of them is exposed on the block layout page as a plugin derivate. There's one plugin class for them and then there are derivates for each content entity. Those are the things you can list with views. Only those.


Everything is connected, you can create custom/content blocks, which are exposes as a block plugin, which is then placed and becomes a block config entity. But they're all different things.