The UK has ruled it out as a solution for large local events and cultural activities, they haven't ruled out vaccine passports in general.

As far as I can tell they're still very much planned for inbound international travel to the UK, and they're already in use for outbound international travel - the NHS app is accepted as proof of vaccination status at the border when entering quite a few countries e.g. Greece https://www.gov.uk/foreign-travel-advice/greece/entry-requir...

I would, er, plan on getting very used to wherever you are now, then. I'd assume most countries will require some sort of documentation on this.

Have you never travelled to a vaccination mandatory country where you needed to prove vaccination against e.g. Yellow fever?