git log ..<branchname>

Lists the commits that are available in <branchname> but not in the current branch

Variations include using different formatting options with --oneline, --graph, etc., or specifying a commit hash instead of a .

git log <branchname>.. lists the commits available in <branchname> that are not part of the current branch.

Both of them are particular cases of git log <commitA>..<commitB> which lists the commits available in <commitB> that are not part of <commitA>'s history.

Specific examples:
git log ..main