I get the want to have bisexual role models and figures in society. I truly do but like when you label historical figures as bisexual just because they had relationships with men and women, you are helping take away the agency of those people in the past and many people currently. You can be straight or gay and had relationships with other genders. Sexuality is fluid. It doesn’t make you bisexual to have been in relationships with men and women but if you want to identify as bi you can. This applies to historical figures as well. The only way you can label someone bisexual is if they call themselves bisexual from their own lips. Anything else and you are mislabeling people and erasing their identities, which we as bi people know all too well so please stop doing that.
But it’s not like many historical figures went round saying they were straight or gay either - so surely putting any sexuality label on a person who lived before these labels existed is mislabelling? I’m just not sure why it’s only mislabelling when we choose to label as bisexual people who clearly had attractions to more than one gender.
Also fluid sexuality is just an experience that some people have, it’s not true of everyone or an experience unique to people who could be called bisexual.
While it’s true that say Julius Caesar — a well know historic figure who carried on so much & so publicly that Gaius Scribonius Curio, another Roman consul referred to him as "every woman’s man and every man’s woman" (see Suetonius “The Lives of the First Twelve Caesars”) - did not dash about referring to himself as "bisexual", it is equally true that the primary reason for this is because that famous general did not actually live in the 21st Century nor did he speak the Queen’s English.
And may we be so bold as to point out that the aboriginal inhabitants of the Americas did not actually refer to themselves as First Nations, Native Americans or AmerIndians. And frankly until sometime in the 10th Century AD no one on “this sceptred isle” called any "blessed plot" of it England either.
However it must be said that one does not frequently hear people incessantly whining that to refer to any of these latter things is ahistorical. It is merely taken as a given, that it is a convenient way to describe various common things so a modern audience might have a clue as to what you are referring to.
Since the very definition of bisexual/biromantic is those who have the ability to have a physical, romantic and/or emotional attraction to other people of various sexes and/or gender identities — as oposed to monosexuals (gay, straight or lesbian) whose attractions are only to those of a single sex and/or gender identity - it seems a bit unclear how you would want historical people who are clearly by their behavior "bisexual" to be described.
And further since sexual fluidity is simply an interesting biological "thing" found in all homosapiens and indeed probably in a great deal of the animal kingdom, but it is only something that is readily apparent in humans (who can discuss it) who are bisexual (because it can sometimes cause some people to wander back and forth across an artificial construct called the gender-line), what all does that have to do with anything, historic or otherwise?
Or is the actual issue (as is frequently the case) that people would just as soon skip the entire subject and we can all go on pretending that everyone everywhere is all just biologically rock-solid stable cisgender and heteronormative?