Honestly, beyond around 10.9, it's been pretty pointless from the end user perspective. Technically, they rewrote the window server to use Metal instead of OpenGL in 10.13 and that did bring performance improvements (and surfaced many bugs in the nvidia driver that they fixed in 10.14 which I'm currently on), but there were no noticeable improvements to anything since. 10.15 aka catalina just brings more restrictions on what you can run. 11.0 aka big sur is a pointless UI redesign.

Apparently, when they run out of technical things to improve and stupid code signing policies to enforce, they redesign the UI because it's a law that if you're making a popular OS it absolutely has to have a major update once a year, no matter what.