Jan & Feb - downplayed the virus - I'd expect any President to do that, the entire point is to reduce panic
March - declares emergency as cases rise, extends the "slow the spread" policies
April - discusses masks, emphasizing that it's optional, not mandatory (needs to say that to retain his base, it's an election year, after all); maintains travel restrictions, but recommends states relax policies
May - mentions that he uses hydroxychloroquine
June - indoor campaign rally
July - continued to downplay COVID saying it'll go away
August - encouraged social distancing
September - continued questioning effectiveness of masks

Basically, he was against masks, in favor of social distancing, and urged rapid development of vaccines (Pfizer vaccine was available around the end of 2020). He took and recommended others take the vaccine as well.

It's impossible to know exactly how Clinton would've responded, but I imagine it would be quite similar, with a bit less rhetoric and perhaps a little more distancing at rallies, just given what Biden did (but it's hard to say exactly, since mask-wearing became a form of speech).

So the main difference I see between Trump and Clinton/Biden is optics, not policy. And given the death rates between states (e.g. Florida vs California), there isn't a clear difference based on the party that was in power, and differences are more easily explained by climate, population density, and demographics. So sure, you can probably point to cases where people contracted COVID at a rally or something, but in terms of policy, there doesn't seem to be much difference between left and right on the COVID response outcomes.

So all in all, I think Trump's rhetoric around COVID was terrible, but I don't think it's fair to pin those deaths on him because they likely would've happened had he lost in 2016.