The change made in#48121 means that it's not possible to route into multiple transport as fallback like

framework:messenger:routing:My\Message\*:[async, audit]

F.e. the messageMy\Message\ToBeSentToTwoSenders would only reachasync.

The comment in the code mentions

if other senders already matchedwith previous types, skip the senders bound to the fallback

While in reality how it works is

if other senders already matched, skip the senders bound to the fallback

After the changes in this MR it works as mentioned in the original comment, meaning it does not skip for the same type, but routes to all transports for that type.

This is not a BC break because anyone who has more than one transport in a wildcard rule has never received anything matching the wildcard on other than the 1st transport – so only if you had a misconfiguration in the first place you're affected.