My existing computer runs Blender 2.93 okay but it gets crashy in Blender 3. (2012 manufacture Macbook)
I no longer have any real reason to prefer the Mac, I think.
Desirable: Lots of RAM and a graphics card
I am thinking preferably 32 gb RAM and an NVIDIA graphics card, but does it really need to be that in particular if something else is less expensive?
One refurbished one I saw checks all the boxes, but it has Windows 10. How much does it matter whether I am using Windows 10 or Windows 11?
I like Linux in principle except when there is commercial software I care about. Should that mean I would prefer Windows 11 to Windows 10 because the "Windows Subsystem for Linux" is more advanced in Windows 11?
How much does it matter whether I am using Windows 10 or Windows 11?Windows 10 or 11 won't make a difference to Blender.
Desirable: Lots of RAM and a graphics card
Don't forget CPU, Lots of RAM is worthless without a decent CPU.
Check out the Blender requirements and base your decision on that and your wallet.
The minimum requirements will run Blender, but give problems with larger scenes and/or particles and physics.
Personally, the recommended requirements is the minimum.
Have a read of this article blender-3d-hardware-requirements-what-you-need-to-get-started-with-blender