As a sr eng, they've also probably experienced a bunch of PMs before, some good, a lot less so, all with their pet projects and agendas that next year will be entirely new and innovative and in the bin in 12 months.
The best ones I have worked with are competent, they dont make me do their work, they keep their promises, they dont waste my time, they see organizational issues and take point on them, and they generally were unflappable in targeting organizational discomfort about tackling an issue or talking to so and so.
This is really hard for someone jr to the space, but humility in the face of everyone's priorities is a great start.