Suppose it were possible to ride your road bike blindfolded. You're experienced riding both Ultegra 8000 (2017) and 105 R7000 (2018) groupsets, and so you ride two bikes that are identical, other than having the two groupsets. Would you be able to determine, just from how frank and crisp shifting is, whether you're riding one or the other?
There is a GCN video about that, it is 105 vs. Dura-Ace, so Ultegra is probably even less likely, but obviously not impossible.
Some other notes
For R7000/8000, Shimano seems to be using the identical hood covers, this implies the same shape and material, so I doubt that you could feel the difference, here. It is the same for previous R5800/6800 generations, I got mine changed on my 105 bike and the invoice also had Ultegra on it for that part. That's at least true for the replacement part but I doubt that Shimano ships 105 shifters with rubber of lesser quality and only offers an "upgrade" spare part. To me, the new hoods feel and look pretty much the same.
If I'm not mistaken, 105 in that generation has an older front mech design that was just updated with trickle-down tech on the latest 12-speed refresh. I can recall this being mentioned in a review, Ultegra upwards was using a different design/geometry on the front derailleur for improved shifting and 105 just got improved later on. However, in my opinion, front shifting might already feel different if you are running different chainrings, FD adjustment is slightly off or you are comparing bikes with different cable routing (and more resistance/kinks in the cables).
Actually, while I don't have experience with 12s Shimano, it may actually be possible to tell the difference blindfolded for 12s Di2 groups.
Shimano's Hyperglide shift ramps are quite advanced and they produce really smooth downshifting (to bigger cogs). The shifts to smaller cogs are less good. All the 11s groups had Hyperglide.
9200 and 8100 have Hyperglide+ shifting. This is said to make shifting to smaller cogs smoother. If true, that's how you might be able to tell 105 Di2 from the other two Di2 groups. That said, the difference might be small. Also, if you specced a 105 group with an Ultegra chain and cassette, that would give you HG+ shifting, although that combination probably won't come on stock bikes.
105 has a mechanical version, and while this is a trivial answer, if you're riding mechanical 12s, you're on 105, Campagnolo, or SRAM Apex.
I just noticed the question did specify 11s mechanical R8000 and R7000. These groups come stock with Shimano's excellent SP41 cable housing. However, Ultegra and DA use cables with a lower-friction polymer coating, albeit this can flake off and jam the shifters, and should be replaced more than the Optislick cables that R7000 comes stock with. I think I can tell a small difference between SP41 housing and the high-end cables versus good Jagwire housing plus good polished stainless steel cables. The difference between the high-end polymer vs the Optislick cables (which are also coated, btw) will be smaller.
Some of the material in this question overlaps a lot with several others. In general, Tiagra may work nearly as well as the performance groups, although it's currently 10s. From 105 to Dura Ace, the most noticeable differences aside from the HG+ shifting are the weight, the aesthetic finishes, and the 105 Di2 shifters having no satellite shifting options. In substantive terms, Shimano says that their chains gain better and better low-friction coatings as you move up, which should result in lower friction and longer life - albeit the last claim was contradicted by some testing for the 11s groups.
A bit beneath the surface, from 105 to DA, 105 has less advanced surface treatments for the cassette cogs, although I'm not sure how big a deal this is. FWIW, I used a DA chain and 105 cassette on my bike. 105 has solid chainrings, and the forging process for the cranks is older (but I think they're still hollow). On the mechanical groups, all 3 groups used Shimano's well-regarded SP41 housing. However, the top 2 had a higher-end polymer coating on the cables that I think produced really excellent shifting, but it can flake off and clog the shifter so it should be replaced more regularly. 105 uses Optislick, which is a less advanced polymer coating.
Below that, the groups would probably downgrade the cables. They'd clearly add weight. Most clearly, they have fewer speeds. We aren't sure how durability might vary. Obviously you can save on material quality and manufacturing tolerances. However, I suspect Claris and Sora have more than adequate materials and tolerances for their expected use cases, which is new cyclists and casual ones. It would be interesting to have someone build up a bike with Sora, ride 20,000 miles on it, and report back. But I suspect this won't get done due to lack of interest.