SERVER-74124 introduced the code to disallow shard keys that contain parts that start with '$'. It turns out that check is too strict since it is valid to shard with a shard key with DBRefs (i.e. $id, $db and $ref).
- is caused by
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SERVER-74124 Disallow sharding with wildcard shard key pattern
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 - Closed
 
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- related to
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SERVER-77255 Shard key field validation for DBRefs prohibits extra dollar-prefixed fields
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 - Closed
 
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