I don't think Putin "fears" Trump. I think he just prefers to deal with Biden, because Biden is a "traditional" US warhawk politician, the kind that the Russians have had to tolerate and deal with for the past 70 years. They are used to dealing with bloodthirsty warmongering assholes like Biden.
They are idealistic neocons, and they act in ways they think will ensure that the USA will prevail in the long term.
Trump, however, is not an ideologue, he has no set frame of reference; he is all about himself, and will do whatever he thinks is best for him at any given moment. Impossible to predict.
And therefore much more dangerous.
Regarding your comment on "political dirt" - we now know that there was a LOT of dirt to be had about Biden in Ukraine. Just as we now know that Hunter's laptop was a real thing, and the operation "Crossfire Hurricane" was alsop a real thing, and Obama was, indeed, spying illegally on the Trump campaign.
I am sorry that you suffer from such a severe case of TDS, but you should not let it force you into condoning illegal actions or government overreach.
And in the end, Trump did what Obama refused to do, which is a fact that seems to have escaped you.
A more important fact that also appears to have escaped you is that Obama refused to provide lethal aid because he believed it could lead to WWIII.
Something that no one in the Biden White House seems worried about.
And that fact should REALLY scare you.