TL-DR
Live life 3-6-5! and get theming before your children or parents
Or don't
I'm only going to add my view on this.. there might be more comments down the line about this subject or there might not.
It's an OK debate to have; why Big Sur is ugly. My take is that there can never be a truce with regards to how and what an UI and UX should look and behave like.
I realize that I am in the hands of Apple and the choices their research and security team does.
Admittedly I'm often perplexed as to how Apple came to the conclusion that so much white-space on the Finder toolbar and the color white is a re-vamp.
I'm a bit confused about System Preferences too. I think it's too crowded there by default and not enough separation and sense in what belongs together. Wasn't there at one point on earlier OS X version a small text that told what is what; i.e security, appearance. Anyway - I'm no expert. My opinions stem from the 13 years of using macOS and their ancestors. I got on with a Lombard(had a another name too I think - Piston or something?!) Mac laptop that had would eventually be upgraded to I think 10.2.8. Fun times.
From that perspective of having gone through all these iterations of macOS and even their naming of macOS - Mac OS X to OS X and now macOS - I get the majority of people voicing their opinion of a forum that still allows opinions to be voiced. This topic isn't the most controversial of topics. It's a topic that's been around for decades on all the platforms I have been in contact with.
Magic Workbench on the Amiga - people loved it or hated it with a passion. Then came some perspective icons for Amiga OS - those were equally not everyone's cup of tea.
There was and still is a theming engine for Amiga OS - believe or not. That was fun too.
Linux users is in all types of conflicts with themselves and other users and don't miss an opportunity to lay down the law on KDE vs GNOME and how one is much better than the other.
Windows 10 - phew, that's apparent I think. Metro/Modern UI - white-space en-masse - squared cornered windows and too many odd design choices with icons dating back to the Stone ages or Windows 98 at least.
The thing about me doing bits and pieces to macOS' interface is no more than a hobby - edit.. I take that back: It's a way of life. A way to keep myself occupied during the day. I have all the waking hours to myself. No wife, girlfriend, children or pets to take care of and no immediate family to tend to as they live their own life and enjoy not having to be interupted by me.
Some would say I am blessed that way. I don't see it like that all the time. I survive on having a good time.
So, I wake up before I go to sleep and make icons and other graphics that I feel is right in appearance for me.
I've used my available fingers to count the number of active macOS users who use my themes and take active part in suggesting and participating in making theme suites for macOS that require SIP to be off and can be applied to the system.
That number? It's 7 (seven) or 8 (eight)
SIP to be off is a big hindrance for all new Mac users (since it's on by default on a new Mac purchase) and for current users that wants stability and peace of mind. Stability is to be debated - peace of mind is very subjective.
Stability is of course subjective too - I just don't think that SystemIntegrityProtection should be what it comes down to if all the issues a Big Sur user has is the appearance of the theme.
I am happy to help, and I have. Not everyone decides the help is adequate because they want all the things done like ordering a pizza.
And that also is another issue.. what I like and see as possible for me to spend time on is very different than anyone else.
Apple does its best to stop us all from doing anything that could see a harming the user's experience so that Apple Support suddenly gets 1200 calls about something called SIP and how it's to be off because of some dude acting like a cool dude decides to stuff a new set of traffic light | titlebar control buttons and stuff down their throat. I can see how Apple would like to eliminate those frantic calls at all cost.
Does anyone remember the Application Enhancer Framework.. I keep telling people that there was a story that The Genius' bar at the time once had one customer come in and explain a boot issue - to which the "genius" at the Apple Store was acting all like "hey, you dumb or something - that APE framework is what is causing your OS X Tiger update to go bad"
That story might be paraphrased a whole lot. In all honesty, I'm certain I've read a story similar to that.
If you want to do something about the theme on Big Sur then there's no two ways about it. It's time to get started and rise...riiiiiseeeeee my fellow themers and get on the MacEnhance Discord server and get an early download of IconChamp - works wonders. PS look in the Pinned Messages too for details on what's new and more