According to the branch permission documentation here:
https://confluence.atlassian.com/bitbucketserver/branch-permission-patterns-776639814.html

Patterns ending with a "/" are treated as a "/**" in Datacenter

Bitbucket Cloud's documentation:

https://support.atlassian.com/bitbucket-cloud/docs/use-branch-permissions/#Branch-patterns

Which allows for a * wildcard at either the start or end.

So when migrating a Branch Permission to Bitbucket Cloud's Branch Restriction the trailing "/" could be converted into a "/*" to be a valid and with matching behavior.