Weird dynamic in new team

[Goatsandgardening]

I've just started a new job, I'm a supervisor and my manager is lovely but comes across as very blasé
I've spoken with him about lack of guidance and no handover, he agreed and said we don't have good governance or clear policies.
I've also mentioned behaviours of some of the team, such as making snide remarks or outright saying I don't deserve to be there they should have promoted from within, etc. He just said that's the culture and dynamics
My manager said he is happy with how I'm doing but I don't know how to get him to take it seriously with the behaviours in the team or the unclear requirements of the role
I've had a bit of time off before this due to family commitments so my confidence is a bit shot, I used to be much more assertive and would have sorted this easily before!

I've also mentioned behaviours of some of the team, such as making snide remarks or outright saying I don't deserve to be there they should have promoted from within, etc

being new in a role can either be really positive or very challenging. New Kid on the Block often gets burdened with the baggage of the team that they had no part in. So the resentment that you got the job that they didn't is an example of that. It's ridiculous, if they were so great they'd have got the job. You were better at interview/qualifications and experience etc, so you got the job.

your manager's dismissal of what you said is because he knows his people, and is probably aware they're a bunch of whingers. He's not going to start rocking any boats with his existing employees by reacting to their silly grumbles.

so it's down to you to get into your role, avoid the office politics and make an impact. Don't get sucked into trying to be best buddies with everyone, it's just a distraction

I do think the fact that they couldn't promote a supervisor from within says something about the workplace as a whole. They either are choosing poor hires, or they aren't investing in and developing their existing staff adequately. There are certain roles which can be tricky to promote from within, but a supervisor isn't one of them.