Even if that was true, this would not solve the issue. Consider if any Trump company decides to pursue a big new project in, oh, say China.
Consider that just the knowledge of that, which might not be more than he might read in the papers, could very well cause him to adjust his policies either in the hope of favours, or even just subconsciously to avoid causing trouble for them.
Beyond that there is plenty of scope for outright blackmail. E.g. what if some Chinese representative whisper in the ear of some Trump employee that significant legal problems might appear as long as China's relationship with the US is still strained over Trumps apparent lack of support for the One China principle. They'd not even need to mention his company, for that matter, or contact him.
A slightly pointed press release about how there will be a crackdown on companies believed to not represent interests that don't fully support the One China principle would work too.
Chances are we'll never find out how Trumps policies are affected (or not) by foreign interference, but it'd be naive to think that there aren't multiple powers that have people considering how they can take advantage of Trumps business ventures presence or prospective interests in their country to curry favour with him or try to pressure him right now.
I know if I was running a country, then at this point I'd have a whole team on looking into opportunities, because even though it'd be rather unethical I'd want something in my back pocket in case Trump were to do something unpredictable that'd harm our interests. I'm sure there are plenty of regimes with less scruples about unethical methods.