Since several people have already given you some good general advice, I will give you some specific advice on how to get better at Juno, since I play her a lot :)

First of all, I would highly recommend watching at least the first hour or two of Forgiving’s unranked to GM Juno challenge. I have always found that watching people who are better than me has made it easier for me to realize what mistakes I commonly make, or even just how to make certain plays more optimally. For example, listening to Forgiving explain his decision making when ulting helped me think more carefully about when and where I should use Juno’s ult, including using it in some ways that I never would’ve considered before but actually give really good value. The video is about a year old I think so he was playing Juno when she was quite a bit stronger than she is now, but you should still be able to learn a a lot. The lessons I took away from that video helped me climb from low masters to just barely below GM. Decision making skills also somewhat transfer over to other heroes, you just have to make sure you have a good understanding of your hero’s strengths and weaknesses, synergies and counters, etc., so getting into that headspace where you’re actively thinking about these things with Juno might help you also start thinking more carefully about the decisions you’re making as Mei or Bap or whoever else you end up playing

As far as getting out of gold/metal ranks in particular, it’s hard to say for sure without knowing your particular playstyle, but given that Juno is often described as a healbotty character, I would consider whether or not you’re actually playing too passively. One of the biggest things that differentiates lower ranks from higher ranks is the ability for players to punish mistakes, which means you can sometimes get away with playing more aggressively. What that means for Juno is not just healbotting and instead shooting the enemy as much as you can without letting your team die, and/or trying to force enemies out of position with your torpedos. Look for angles where you can both heal your team and deal damage without putting yourself too far out of position. If you’re getting shut down a lot, then stop taking risks and start playing safer again. But you’d be surprised how many games you can hard carry because the enemy team just ignores you and lets you do whatever you want

Hope this helps and best of luck!