Branches: main and feature/squish
First work in feature/squish and push + created Pull Request.
Then go to main: $ git checkout main && git pull origin main
Set rebasing correctly: $ git config --global pull.rebase true
Check-out your feature branch and ask for a rebase: $ git rebase -i main
In the VIM rebase file, type 'i' in order to insert fixup = like "squash", but discard this commit's log message. Only 'pick' your oldest/first commit - and 'fixup' all the others, but do a 'fixup -C' in order to keep the text of your last commit message, if that is the text you want to keep. Hit 'Escape' and type :wq to save and exit.
pick [1] Ugly commit message
fixup [2] Ugly commit message
fixup [3] Ugly commit message
fixup -C [4] Clear good message
This results in just 1 commit with the Clear good text.
You will probably be able to do a $ git rebase --continue from the usual terminal here, and after that get the $ git status to see your remote branch is diverging, which is good, then $ git push --force-with-lease and you should be all set and ready to merge.
Or use the GUI of Github:
Badly explained: https://www.maykinmedia.nl/blog/2017/nov/20/git-rebasing-make-your-commit-history-pretty/