You can use git switch - to switch to the previous branch. In the following example, we see switching back and forth between branches main and my_dev_branch:
C:\git\my-repo [my_dev_branch]> git switch -
Switched to branch 'main'
Your branch is up to date with 'origin/main'.
C:\git\my-repo [main ≡]> git switch -
Switched to branch 'my_dev_branch'
C:\git\my-repo [my_dev_branch]>
Edit: Old habits die hard. Updated to use switch instead of checkout since switch has a clearer responsibility. Obviously they work exactly the same for this scenario.
Note that
git checkout -/git switch -examine reflog to find previous branch. Which means if you renamed the branch, at least current version of Git would be unable to rungit switch -.