And please also share why not just use e.g. 256-bit UUIDs instead of v4 128-bit if collisions really are a problem with 128-bit (which i find hard to belive).

I think for the same reasons that 128bit ones can collide, any amount of bits could. I don't have a perfect understanding of the math involved so I could be wrong.

Here is one of the X posts I was referencing: https://x.com/initjean/status/2054281688801321457?s=20

Basically in theory you could generate 1M UUIDs per second and never have a collision for the life of the universe. But in practice due to bad entropy some collisions have been seen in practice. I made the service in part as a joke off of this discussion, but also in case anyone may actually want to use it, it will dutifully provide the advertised function.