Would an ancient virus be any harm to modern humans? Or would we be too different to what was around millions of years ago for it to be a le to survive and infect people?

I think so. We can be modern, but we still breath exactly like any other mammal, including prehistoric species. Our methabolic routes are shared with lots of other species, extant and extinct

I'm guessing all kinds of viruses and bacteria that evolved to infect whatever was living 90mil years ago.

But there's always a chance of also finding a buried spaceship.

or a stargate ;)