Forking
If forking a repo to make a PR and you intend to keep fork around then it’s advisable not to commit to the main branch to avoid issues with history not being able to be linear.
I normally set branch protection on the main branch as shown in the screenshot.
This still allows it to be updated from the upstream but not committed to directly.
Note: If Do not allow bypassing the above settings is not checked it is still very easy to accidentally commit to main.