I've never worked on a team that had conventions for both commits and PRs. In general, the goal of such things is to help trace work across multiple systems, and for future research trying to track down old changes. All the places I've worked or consulted, they do that at the PR level, not the commit level. So PRs will start with a ticket #, commits are freeform.

That being said, some places do have commit standards. Just ask the team what they do when you start somewhere. Don't bring conventions in where a team doesn't use them - it just adds noise. If you or the team see how adding conventions can benefit your work, talk about it and make a decision together.