$convert now supports conversions between string and BinData. These conversions must specify a top-level 'format' argument, which can be any of the following: "base64", "base64url", "hex", "uuid", "utf8". A new $toUUID shorthand expression was introduced to convert UUID strings to UUIDs, and $toString now supports BinData input.

Description of Linked Ticket

Since $convert doesn't work with BinData types, and there are no helper functions for binary data, nor for UUID in particular, it's very difficult to do something like converting UUID that's stored as a string to a proper BinData format.

Example: I have string "867dee52-c331-484e-92d1-c56479b8e67e" and I want to have UUID("867dee52-c331-484e-92d1-c56479b8e67e") which is BinData(4, "hn3uUsMxSE6S0cVkebjmfg==") and there doesn't seem to be a way to do that server-side.