Every writer has their M.O but if there is one advice I am going to give (and you know, if you think I am worth taking advice from), I would tell you to know your MC character factually at least before you start writing their story.
You may think this would be obvious but you would be surprised. I am not saying that you have to know the colour of their eyes or their physical measurements (which you do) but that you have to engage with your MC on a deeper level.
A person is the combination of nature and nurture. Their landscapes shape them as much as the people around them do. So have a conversation with your MC before you start writing their story. What’s their favourite colour? What’s their deepest fear? What flavour of ice cream do they prefer? Sometimes what they don’t like is more revealing than what they do.
Are they afraid of the dark? If yes, then why? Is there a childhood trauma or incident? Do they have any triggers? There’s no reason your main character cannot be as complex and layered as a person.
Chances are, figuring out your protagonist will give you insights into the story you are writing. So open a word doc or a fresh notebook and have that conversation with your MC. Write your notes. Watch them grow and come to life before you. It’s a grand feeling when they do.