It came out in December that his taxes were being investigated and it was widely reported. Easy to see from the wikipedia article where there are multiple citations from major news outlets.
> It is materially interesting what business connections the US president has with (famous for being corrupt I might add) Ukraine.
What is interesting? You're playing connect the dots and taking possible tax issues from business in China and connecting it to made up stories about Burisma and saying "now prove me wrong". Again, the impetus is on the person making the argument to make an actual concrete claim. The Senate republicans already have you covered on the Ukraine part, of course (nothing).
> otherwise the decisions don't make a lot of sense
Henry Kissinger got a bunch of people to heavily invest in Theranos. You're going to need more substance than "why do rich white people keep failing upwards?" for a story here.