That's right, and for GitLab `glab mr view -w` will work. I wanted to have a tool that works with both and lets you open in browser whatever you're currently looking at. So it opens the PR for current branch, repository home page for main branch and PR creation page for new branch. You can also open the repository with `git open` [1], and create a PR clicking the link you see after pushing to GitHub/GitLab, but the goal was to have all three in a single command.
[1]: https://github.com/paulirish/git-open