In that case, I first commend you for the clear amount of work you've put in to training. Being that heavy, at that BF%, you probably look titanic.
Secondly, in your case, I'm with
@Kozushi and recommend you stay away from this skill. The goal of working up to more Pull-ups is certainly great, and you definitely have some kilos to lose if you choose (at 92 and, say, 13% BF, you could lose 5 kilos of fat and end up at 87 kilos and 8% BF, without having lost any muscle mass for instance). But I wouldn't place One-arm work as the end goal, personally.
There are people who can do it without injuring themselves. I think it is down to genetics and body proportions combined with correct exercises. Some people have their primary muscles mass in their upper body. For them it should be easy. Besides distribution of muscle mass across the body, ligaments, tendons, body proportions should also be taken into consideration. I have my primary muscles mass around my femur bones and glutes. Rest of my body is more average no matter how hard I work them.
Those people aren't 90 kilos. They are 60-80 kilos, usually towards the lower end. Genetics, proportions, age, sex, they all play a role, you're right.
And btw on a lighter note, to
nobody is the One-arm Pull-up "easy". I like the SF analogy of strong vs weak arm. The OAP is hard for those built for it, and hard
er for those who aren't.