There was no appearance of impropriety. That claim wasn't even considered until Biden Became Trump's political opponent. Can you show a single reference to that claim before Trump started whining about it?
There's a
shitload appearance of "impropriety". It just came up recently because a new president was elected in Ukraine, a president that has promised to root out corruption.
Just be honest. Admit it. You don't want an investigation because you're afraid that it might demonstrate that Joe Biden and son Hunter were engaged in corruption.