Trust Apple to screw more things up with every update.
For many years, I’ve relied on tab groups to load all at once. I can quickly scan things by closing the tabs one by one, eg stock charts.
Now with the latest Safari update on macOS Big Sur, Safari only loads the visible tab. All other tabs just sit there and do nothing until clicked, whereupon I wait several seconds for each tab to load. That’s on top of the confusing and ugly new tab display. But on macOS Mojave things work as they always have.
It takes award-winning stupidity or incompetence to shit the bed this badly. Count on Apple to keep ruining stuff.