Big Sur seems more like a 'transitional period' in UI, combining both flat and 3D UI depth. Similar things happened only in the reverse with Android when going from 2.3 to 3.0 (and 4.0 on phones).
I wish there was at least a 'classic mode' during the whole iOS 7 update similar to the PowerPC "Classic 9" mode to help ease the transition and because a lot of apps either broke in iOS 7 or were inconsistent since a lot of 3rd party apps remained skeuo until updated later to work better with iOS 7's UI design.
I was surprised they even bothered at Apple given Microsoft essentially failing hard with Windows 8. But oh well, life goes on, I got my skeuo back via old Samsungs, and Big Sur is a hopeful sign of skeuo's return on my Mac. I have no real proper replacement for my Mac so I want to have a UI that doesn't hurt my eyes, so far, Big Sur is getting there. We will see next update, I suppose.
When iOS 7 came out, I didn't follow the news, so I expected not much to change as before, and when my devices updated, I thought they went into safe mode given the lack of color and flat icons. When doing searches online, and asking in iMore, the Apple-oriented variant of Android Forums, I was told both 'that's they way OS is going' and 'get used to it.' Sorry, but I cannot get used to something I hate. I have tried multiple times to use it, to give it a chance (and also give modern Android a chance) and every time it bothers me, as those device are no longer fun to use, and I merely tolerate, not enjoy, using them. Now more recently OEMs remove features but mark up the price a lot more than it's worth, and losing headphone jacks, IR blasters, and removable batteries, all once cited as strengths of Android over iOS, are just unforgivable. I tolerated the fact Apple didn't have removable batteries given they lasted a long time, but on Android it's unforgivable. Today's devices all look alike, the UI is pretty much alike as well where at first, you can't tell Android from iOS if a newbie, and everything is too dumbed down. Also there's no modern phone out there less than 5" in screen.
I don't even like modern Samsungs. I have given them and modern iOS devices such as the iPhone X and mom's 11 Pro, but they don't fit me at all, and I hate the UI. So it's not like I never tried. I tried, and kept going back to my old phones. Maybe one day something will push me to go forward but right now, I just don't see a reason to update, since nothing any modern devices do today have half the features I still use, are too big, and the UI is utter garbage. I am not sure if it's intended for younger folks to use since they never went through the first iteration of flat UI design, so to them skeuo is 'old' and 'designed for grandma' but I just can't stand flat design. I have to be 100% happy with what I use, I'm smart enough to not get hacked or install shady apps, so an outdated OS is not going to be unsafe for me. In fact, the last newer device I used, a Galaxy A01, running Android 10, leaked my phone number where I was getting a ton of spam texts from email addresses I couldn't block, so I pulled the SIM, waited a few weeks hoping they would stall at the server and the folks sending them would give up after, and popped the SIM into a Galaxy SIII and so far no more spam. So in fact I got hacked much faster and easier with the newer phone, although I did nothing to cause it.