I'm still comparing them; unfortunately they are in completely different parts of the house. Also, the Q90R is a 65" whereas the Q90T is 55". Not that there should be much difference in PQ between the sizes.
I am truly amazed at how well the Q90T handles blooming with allegedly only 96 zones versus the 480 on the Q90R. Very little clouding with subtitles. Real content shows very little blooming or clouding. Black bars on 2.35 movies are close to equal in terms of light bleed, but I still give the edge to the Q90R in this respect. I can see ever so slight bleeding into the bars with a brightly lit area adjacent to it. I don't think anyone but the most discerning videophile would notice, however. With 4x3 content, the vertical bars are not as black as I would like; not as good as the Q90R but far better than my Q8FN.
Screen uniformity is better than the Q90R, but I realize this varies by the panel. The Q90T is also a light cannon, not that the Q90R is a dim tv; it is not. However, I run my Q90R backlight at 40; my Q90T is at 30.
Shadow detail is far better with the Q90T settings OOTB. Since black levels are more important to me than shadow detail, I actually reduced the "Shadow Detail" (formerly "Brightness" on the Q90R) setting to deepen the blacks.
One other noticeable difference from older QLED Sammys I own is how the built in apps present streaming content. I personally like the Roku Ultra over the internal apps, but because I think the upscaler in the TV is far better than the one in the Roku, I set the Roku to 1080P for HD content. Then I use the built in apps for 4K rather than switch the output on the Roku constantly. On all my Sammys before now the 1080 HD content looked pretty much the same regardless if I streamed thru the built in app or the Roku. With the Q90T, the 1080 streaming content is noticeably softer than the same from the Roku. The 4K HDR looks great, however. This is no issue for me as I'll just continue to use the Roku for 1080 sourced programming.
In summary my stance so far is that the Q90T is far better than the Q8FN, roughly equivalent to the Q90R, not quite as good as the Q9FN (which is still my all time favorite LCD based display). And from what I remember since I returned them, far better than the Q80R and the Q900R.
I hope this brief summary is helpful to someone.