I am struggling to shift some behavior that is getting in the way of my own career growth and I am hoping to get some insight from others.
My previous manager was a micro-manager and to satisfy him, I ensured that I focussed solely on a few projects a majority of the time. However, my current manager wants to give me room to be as independent as I'd like to be. This means that I now have room to influence and help others, which is fundamental for growth. But now, because I don't have someone asking me for details of how I spend every moment of my time, I question whether any task I do is the highest priority task I should be doing, which takes the joy out of helping/mentoring others, because I know that time can be spent focusing on my own deliverables. This second-guessing is causing a great deal of mental load for me. I also feel like if I ask my manager too often whether I am prioritizing correctly, he might feel like I am not behaving like a senior engineer. Any thoughts on how I can get out of my own way here?
You should ask your manager! Like with many things, there's a spectrum here and a balance to strike. Of course, asking them every week if you are prioritizing things properly would be annoying and not a good sign concerning your independence. However, the extreme of never getting their input is very bad as it's easy to become misaligned and miss the forest for the trees.
I recommend asking them every 1-2 months. I actually think this is a good signal coming from a senior engineer as it shows that you want to maintain alignment and have the proper high-level view of the team and its roadmap.
Going deeper, you should build a strong understanding of team goals/charters/OKRs and orient yourself automatically around those: "How to figure out what the most important projects are?"
This second-guessing is causing a great deal of mental load for me. I also feel like if I ask my manager too often whether I am prioritizing correctly, he might feel like I am not behaving like a senior engineer. Any thoughts on how I can get out of my own way here?
One thing that will help is thinking about the end goal and working backwards. The end goal might be improving a team OKR, working on projects with enough scope, or mentoring "x" other engineers. This will give you confidence about whether you are working on the right thing.
When you have 1:1s with your manager, make use of your 1:1 doc to outline exactly what you are planning to do and what you've done. This will hopefully remove any ambiguity about what you are working on since your manager is basically signing off on what you've put in the doc. Your manager should flag any work that's not high priority and help you course correct if they think you're going down the right path. It's okay to go over who you are helping to mentor and how you are helping them.