What
Delete all local git branches except the one you want to keep (master or main).
Why
Feature branches pile up after merges and clutter git branch output. Check out the branch you want to keep, list local refs, and exclude that exact branch name. Preview the list before using -D, which discards even unmerged work.
How
git switch master
git for-each-ref --format='%(refname:short)' refs/heads | grep -vx master
After you verify the preview, delete the listed branches:
git for-each-ref --format='%(refname:short)' refs/heads \
| grep -vx master \
| while IFS= read -r branch; do git branch -D "$branch"; done
Replace master with main in all three places if main is your keeper branch.