Identify merged branches

# View merged
git branch --merged

# View merged remote
git branch -r --merged

# View unmerged
git branch --no-merged

# View unmerged remote

git branch -r --no-merged

The above cases run the merge check from the point of view of HEAD as this is the default.

But we can also run it from any branch.

git branch --merged non_head_branch

Demonstration

We have the following branches

git branch

* main
key_feature
another_feature

The branches other than main, have not been merged:

git branch --merged

* main

Just to confirm:

git branch --no-merged

key_feature
another_feature