Revert UI on Big Sur?

How can I revert the Big Sur UI changes, especially Finder's?

While it looks cleaner, it now takes 2 clicks to change the Finder's view type of gallery, list, icons, or columns. I would rather have the old UI and use 1 click.

How can I accomplish this?

You can revert application toolbars to their 10.x look by setting NSWindowSupportsAutomaticInlineTitle.

defaults write -g NSWindowSupportsAutomaticInlineTitle -bool false

-g sets this globally (all applications), or you can specify a bundle identifier for a single app. Restart the application for the change to take effect (restart Finder with killall Finder).

However, I think your Finder window is too small, it's still just one click to change those settings with macOS 11 UI.

I would say that even one click is too much. It's waste to raise your hands from keyboard. Instead of clicking there are simple keyboard shortcuts for views in Finder: