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Instead of block plugin derivatives, that expose each feed and category as a separate block in the block library, that information is now stored in the block instance configuration.
There is only a single aggregator feed block, that then provides an option to select the feed that should be displayed. This allows to display multiple, differently configured aggregator feed blocks for the same feed. Same for category blocks.
The feed setting that allows to control if a feed should show up as a block and with how many items has been removed.