You're right that Windows 10 is "generally okay" on an old CPU, even for relatively heavy dev work. But I just upgraded from i7-3770k to i9-12900k and it made me realize how much time I spent _waiting_ for every little thing. I've been switching back and forth between the two as I migrate, and the old CPU definitely feels like a dog to me now.
Aside: I was planning to switch to Linux too, but apparently this CPU/chipset is "too new" for Ubuntu to work, so I'm stuck on Windows for a few more months.