I tried searching "SSE2-4.x" and this is the top result in DDG and Google, so I was initially confused what instruction set the article is referring to. However, this appears to be shorthand for SSE2 through SSE4? Perhaps a rephrasing of the article title could be helpful.

Author here - yes, it's shorthand for the set of SSE2, SSE3, SSSE3 (not a typo), and SSE4 including SSE 4.1 and SSE 4.2. My bad for confusion!

That set matches the x86-64-v2 x64 microarchitecture level. Most of the articles uses 'v2' or 'v3' or 'x86-64-v2', but I thought that more people would be familiar with the names of the instruction sets than that x64 was versioned. The versions only appeared quite recently (2020) and are rather retroactive.

I read it as SSE2->4.x.

Generally speaking, when working with SSE instructions you'll end up using a mix of instructions from 2->4 as they are all effectively just additional operations on the SSE2 registers.