I had a mentor that was the team lead for another team that I wasn't on, but worked in close-ish proximity to. They were great for bouncing technical ideas off

I had a mentor that was the team lead for another team that I wasn't on, but worked in close-ish proximity to. They were great for bouncing technical ideas off of because they were neutral and unbiased. I could agree or disagree with them on any topic and it wouldn't matter at all and since they're not working on the same thing they don't bogged down by the real constraints and could just give their opinion on what the ideal solution is. I think what made it successful was their willingness to listen to other peoples' ideas and problems even though they didn't have a stake in them, and my willingness to be open and frank with someone outside of my team. I've met a lot of devs. that want to project an image of utter competence to everyone around them and I think that precludes them from learning from the experience of others. There's a piece of advice out there that says: Don't go to an engineering meeting with a proposal unless you've already got the majority on board with your plan. Having that sort of mentor/mentee relationship with the senior people on adjacent teams is how I followed through on that advice.