As discussed here https://community.atlassian.com/t5/SourceTree-questions/Windows-2-0-version-easy-way-to-copy-paste-branch-tag-names/qaq-p/581912/comment-id/14249#M14249

In the 1.x version I would select a commit and down in the area with the commit text, commit ID, author, etc. there would be a list of all the branches and tags pointing to that commit. It was easy to select and copy a branch name out of there for pasting into git commands in a console, etc. Now that branch/tag info is no longer showing up in that area of the UI.