> This is the first time that I hear power to gas described as vapourware. I'm very interested in that topic, could you give some more details or pointers?

Surely the onus is on whoever is claiming the technology does exist to provide some details of it.

I checked Wikipedia though [0] and the world's total installed P2G capacity looks like...less than 100 MW? It's at best one step above vapourware.

[0] https://en.m.wikipedia.org/wiki/Power-to-gas