Summary:

Manipulating the repository using the below API works except for the PUT method.

That is, it is possible to READ and DELETE a repo using its UUID, but the update fails.

The below API call using the team name or username and repository UUID works.

curl --request PUT --url https://api.bitbucket.org/2.0/repositories/{accountName}/{repoUUID} -H "Content-Type: application/json" -d '\{"is_private": true,"fork_policy": "no_public_forks"}' -u username:app_password

The below call with empty field and repository UUID does not work:

curl --request PUT --url https://api.bitbucket.org/2.0/repositories/%7B%7D/{repoUUID} -H "Content-Type: application/json" -d '\{"is_private": true,"fork_policy": "no_public_forks"}' -u username:app_password 
{"type": "error", "error": {"message": "No user with username \"{}\"."}}

The below documentation says we can use empty field and repository UUID to make API calls.

https://developer.atlassian.com/bitbucket/api/2/reference/resource/repositories/%7Busername%7D/%7Brepo_slug%7D#post

https://developer.atlassian.com/bitbucket/api/2/reference/resource/repositories/%7Busername%7D/%7Brepo_slug%7D#post

Workaround

Call API using /repositories/{username}/{repo_slug} instead of using /repositories/{}/{repo_slug}