There is no need for it or one way a birth plan needs to be set up, but I recommend a bullet point list, starting with what you think is most important for them to know about you.
This has likely changed over the years and there will be COVID specific things to think about that you'll need to discuss with your antenatal midwife, but I've seen it recommended to consider listing: any medical needs they need to know about, preferences if any on pain relief both for labouring and if you needed to go the OR, if there is a birthing partner, who they are and if they want to cut the cord, preferences for managing the third stage, if any, thoughts on student observers. I also recommend listing any fears or concerns & how you'd like to manage them.
In my earlier pregnancies, I had the typical preference list with all the things and then some. I found this not very helpful and not much was done with it. As pp said, a lot isn't in our control and I think while it can feel informative to go through all the options, it can also be a source of added stress.
In my latter pregnancies, I essentially wrote a "I'm terrified and here's why, please be kind' plan rather than a birth plan. It's a 14 short bullet point list, where I focused on my feelings/fears/concerns, how I wanted to handle those concerns and manage my medical needs, the things that were most important to me and my well-being (including medical conditions & things that put me at higher risks), and common admin questions like students observing and things in previous pregnancies.
This was far more useful even if some bits weren't really followed. It had all the most important to me information right there, and - while it looks a bit silly now - I think briefly if repeatedly touching on my anxiety, fears, and feelings of vulnerability and history of medical abuse and how I cope with that gave them a better grasp of how to help me when I did have a panic attack during late stage one labour.