Right, it's clearly a contested idea, but this article details what it might look like. It doesn't advocate a complete democratization, but one in which a veto is tied to atleast one other country, so not unilateral (among other things). Don't get me wrong, I highly doubt this will ever happen in my lifetime, but it's not an unreasonable notion in and of itself.

https://foreignpolicy.com/2020/09/17/decolonizing-united-nations-means-abolish-permanent-five-security-council/