There seem to be several factors that each tilt an individual slightly towards same-sex attractions. Some are genetic, some are hormonal, and some are environmental. Studies of identical twins, who would probably share all three considerations, have found that the pairs do not always match in orientation.
One of my best friends is the youngest sibling with three or four older brothers. Another best friend has three straight older brothers (including a fraternal twin) and a straight younger brother (fraternal twin of their only sister). I have a older and a younger brother who are both straight.
None of the studies I’ve ever seen has ever suggested that they’ve discovered an absolute cause of homosexuality in humans.
Personally, I believe that sexual orientation in men is similar to handedness. I think it’s a J-curve with most men being straight, a much smaller percentage being Gay, and an even smaller percentage being bisexual. But the studies of bisexuals sometimes indicates a majority of men, and sometimes indicates a tiny minority. I think it relates to the questions asked. Are they counting behavior or identity. There are men who identify as Gay, but have had sex with a woman. There are many men who have had sex with other men, but identify as straight – epidemiologists coined the term MSM to encompass all men who have sex with other men regardless of how they identify (Gay4Pay is just one variety).
This topic is very complex and understanding it might shed light on other topics. Clearly it is controversial even within the LGBTQ+ community. Should there be topics we ignore just because they make us uncomfortable?