For all its faults I think it's strange to criticize Microsoft for maintaining backwards compatibility.
It is a combination of a vertical and orizontal menu. Something like Edge with horizontal and vertical tabs in the same window
It changes its height dynamically by state of each shell extensions. how come it is consistent from a UX perspective.
Here's a MS blog post explaining why they want to move to IExplorerCommand: https://blogs.windows.com/blog/2021/07/19/extending-the-cont...
Frankly, this just follows all the same problems that MS has had with since after W7. Their own APIs have a lot of warts and problems, but MS has not been able or willing to follow through on the migration required to actually move to a whole new API. This has shown up in their Windows GUI frameworks, it's the exact same problem with the Control Panel vs Settings, and here it is again.
I can sympathize with many of the stated goals/benefits, and I can understand the technical difficulties with transparently porting registry craziness into their new framework, and infact I applaud that their fallback is "perfect" - it is just the old context menu. I just wish there was a setting toggle to set the default.