I drove a 2020 Prime and a 2016 Avalon tonight. The Prime is a much more practical car, but the Avalon has that smooth ride that I want. Assuming you own the car, and can do anything you like to it, can a Prime be made to ride smoothly like an Avalon?
I ran my Prime's tires at 35 PSI and it was very smooth. Not a lot of other things your can do and there's really no basis for comparison. Too many other variables.
not an expert in new car suspension but I'd start with all the part #s and good pics of all the suspension parts who's settings/strengths would effect ride softness (the springs and shocks, struts). If the Avalon has same size and shape (swapable) but diff part #s that might be pretty easy. 98% of suspension "tuning" will be going the other way, making ride stiffer, so might be hard to find expertise but I've heard lightening springs (coil or leaf) by removing material with grinder is doable with a little time and patience. Shocks can be tuned with diff weight of oil, and/or diff size passages. But my guess would be shocks and struts for Prime will all be gas pressure and wont take well to disassembly. Call a "tuner" shop and ask if they make adjustable parts that will work on Prime, such as "bagged".
If you want smooth ride test out a recent Lexus ES300h. The smoothest car I test drove....just super quiet and soft. Too isolating for me but wow its impressive. A Prius is like a tin can in comparison.
The Avalon's smooth ride is down to its long wheelbase, higher weight and wider tires with larger contact patches. You can add weight and change to larger, cushier tires. Expect MPG to suffer, still won't be as cushy.