Here's my story about the features I lost between 10.8 -> 10.9 -> 10.11 -> 10.13.
tl;dr Web Sharing, Notes sync, iCal sync, HFS+, apps sync.
https://news.ycombinator.com/item?id=26245164
I gained NVME drivers for using larger SSDs, so tolerated the changes, but I'm not sure if I'll be able to make the leap to ARM M1 if Big Sur is holding me back so much.