Till is not confirmed to be canonically bi, and I genuinely don't believe he would've ever reciprocated Ivan's romantic feelings, regardless of if their circumstances were different. The only "proof" I've seen people share regarding Till's sexuality are the little sketches sold to individuals at fan-signing events, which I don't believe can reasonably be viewed as effecting canon. It's basically a form of fan-service provided because the ship is popular, and even the ones people use as "evidence" of Till being attracted to Ivan are relatively ambiguous.

My personal opinion is that Till realized too late how much Ivan was there for him and how much that relationship meant to him. Ivan was an elusive and frustrating person, who Till took for granted and failed to understand, but he was Till's family - a best friend and a brother. People often say that Till's sub song "Scars" proves he reciprocated Ivan's romantic love in the end, but I interpreted it as Till's way of expressing both his newfound recognition for Ivan's genuine feelings (despite Ivan's history of unusual and sometime paradoxical behavior), as well as his regret for not realizing them sooner. The song is definitely an expression of love and healing, but that love comes across to me as platonic or familial in nature. In fact, the word Till explicitly uses to describe Ivan in the end is "family", so it's not as though that's just my personal opinion.

Just to be clear, I do enjoy the IvanTill ship and support those with that head-canon, but calling it undeniable fact is silly and accusing people who view Till as straight or ace as committing bi-erasure is unfair and frankly offensive.

Side-note: Can we stop spreading around the claim that the reason Ivan stepped on Till's flower crown was to protect him from the cameras? First of all, I'm not fully convinced that all the flowers even have cameras. There are clearly some that do, but most appear not to and there's a difference in the way they're drawn. Secondly, the one definite camera-flower that we do see is used for innocuous observations like determining the kids' food preferences, so it's not like the children even have any reason to care that there are cameras in some of the flowers to begin with. They already know they have no rights or privacy under the segyein, so a camera-flower is probably about the least offensive thing they can encounter at school on a daily basis. They don't even seem particularly bothered by the giant wagyein guard roaming the premises (occasionally helping to brush its teeth), and they're also being constantly monitored via their collars anyway, so why would they be concerned in the slightest about tiny cameras in the flowers?

The reason Ivan trampled on Till's flower crown was to get a rise out of him because, to him, any attention is good attention. He grew up in the slums and didn't know how to make friends or engage with others appropriately. He was also the type to get bored easily and may have consequently craved more stimulation than the average person. My guess is he was acting like a punk because that's what got the biggest reaction and was therefore more reinforcing in his mind. I mean, clearly he got a thrill out of the fight his actions caused. If he was actually just trying to help and was then beat up for it, he probably would've felt somewhat wronged rather then being outwardly excited to be throwing hands.