The PM's role inside a sprint can vary depending on the company, project, and team dynamic. I've been on several teams, and here's what I have found to work the best:
Enable and empower your team - The best way to do this is to get your dev team involved in the discovery process (to an extent). The more market context a team has, the more empowered they are to make decisions without needing to chase you down for every little thing. Invite a member to a customer phone call, ask them to listen in on a sales demo, and educate them on customer problems so that they know WHY they are building the solution. (Ideally, they are involved in creating the solution to a customer problem.)
Write effective User Stories - The stories you write should be detailed enough that the developer can understand what needs to be done, but not so detailed that it feels like you're writing tech specs and feature tests. I have found that Gherkin is the clearest way to illustrate what the story should accomplish, but you do you. Ultimately, it should be to the level of detail that the team needs because, after all, it's a team effort.
Be a snowplow – clear the way - If you don't have a scrum master on your team, you are likely acting as both the PM and scrum master. Even if you DO have an SM, do what you can to clear the way for the team to accomplish the sprint goals and stories. If they need info from you, don't be the blocker.
Never promise exact dates (seriously, never do this) - yes, we commit to stories/points for a sprint, but things happen and sometimes we don't hit a target. This is why you should never ever ever ever ever promise a completion date to the business. You're doing the team a disservice and making them look bad. Be ambiguous with target dates.
Celebrate wins - retrospectives are an important part of a sprint. It is important to team morale that you celebrate the team's wins and accomplishments. After something is launched, I like to share KPI's with the team during standup so that they can see the impact they made on the business. Especially in 2020, celebrate the heck out of your team.