I support gender equality but doesn’t the fact that women have been oppressed throughout history suggests they are the weaker sex?

I actually don't know why this is. In terms of physical strength, it's obvious that men are the stronger sex and that could be the root cause. I think there's an argument to be made that this happens simply as a result of the fact that men tend to be more manipulative, and millions of manipulative people over the generations leads to a manipulative culture which benefits the more manipulative population.

Yuval Harari has an interesting discussion of this in his book Sapiens (or somewhere :) ) and comes to the conclusion that we really don't know why oppression of women has been so widespread. He notes that it is true that men, on average, are physically stronger than women, on average -- but that doesn't really explain this pattern, since it isn't usually the physically strong men who are in charge of society. Front-line soldiers should be physically strong, but the generals and politicians who send them into battle often are not.

I don't have a good explanation for this bad pattern either. I only hope it is changing.

It's a good question. My thinking is that it comes down to physicality. We're animals. Historically it was males who hunted and females who took care of the "home." There's a power balance that came to be which allowed men to draft the 'rules.' There have been matriarchal societies throughout history, and some still exist, but as humans started to migrate they were generally communities run by men. And when more organized religions were created, it was men who decided who the gods were and the rules of behavior.

objectively speaking yes that would make the most sense.
Truth is that women could not and can not do to men what men have done to them through out history, no matter how hard they try now because realistically most men would fight back against it at a level that women I believe for the most part would not be willing to go themselves and I dont say that in a bad way because I honestly am not for men being over women or women being over men.
Just that men and women are very different

It may surprise you to know the Bible calls women the “weaker sex”.

Define "weaker"