What is bipolar caused by

Im looking at causes of bipolar and while there isnt a single cause there are things that make it so that a person is more prone to developing it. For example, abusing substances, childhood trauma, genetics, stressful event, etc However, im thinking about me and why me. No one in my family has bipolar and i had a pretty ok childhood. My parents worked a lot, but i always had something to eat, got presents on my bday, went on trips, etc. My parents were also present with me when they could, but i did spend a lot of my time with a nanny. I did smoke weed a lot for like 6 months of my life but thats pretty much it. I am, however, a big drinker, started when i was like 16 and used to struggle a lot when i was 18-20. I am doing much better now. But still, i have a hard time figuring out what caused my bipolar. Like, did i have a somewhat traumatic childhood without realising? Was i neglected? Definitely my substance use played a part, but i have a hard time imagining it is the sole cause of my diagnosis. Anyways, wanted to know for you guys what do you think caused your bipolar disorder or something and what you guys think about mine.