Add the remote, call it "upstream":
git remote add upstream https://github.com/whoever/whatever.git
Fetch all the branches of that remote into remote-tracking branches
git ls-files --others --ignored --exclude-standard
source: https://aohorodnyk.com/post/2023-11-28-list-all-ignored-files-in-git/
To squash multiple commits into one, you can use Git's interactive rebase feature. Here's how you can do it:
git rebase -i HEAD~9
$ gh config set git_protocol https -h github.com
$ gh auth status --show-token # <== copy your authentication token
$ git credential reject <<<"url=https://github.com"
$ git credential approve <<<"url=https://USER:TOKEN@github.com"
source: cli/cli#1326