Maybe Trump is enamored of business opportunities in Russia. Who knows? I do not think anything beside extraction of oil and gas is going to be very lucrative. The place is a mess.
As for "allowing" Russia to keep the land it has grabbed, what is the alternative? Mexico "allows" the United States to keep California, Arizona, New Mexico, etc., but does Mexico have a realistic alternative?
Who is going to pry that land out of Russian hands? Ukraine is losing more land every day. The Russian offensive does not look like the blitzkrieg of the summer of 1941, but it is more like a steamroller, slow but inexorable. Thus, the pressure is on the side
losing ground to make a deal while they still have a country. Are the negotiators supposed to say to Putin, "You would better make a deal because if you wait until tomorrow, … you're gonna get
more land. And if you wait till next week… You're gonna get
even more land."
To continue indefinitely is to become Palestine, the people who refused to make a deal.
For reference, here is the America First Policy Institute plan developed by Lieutenant General (Retired) Keith Kellogg:
America First, Russia, & Ukraine
That is probably the point of departure for any peace plan, although this was written last April. I am not endorsing AFPI or Kellogg, just pointing where you can read more.