When using Vue as a detached SPA, surely there aren't going to be any major 'vulnerabilities' discovered after its EOL in Dec 2023.
My use of Vue is as a detached front-end SPA, with an Express REST API backend, practically all the 'risk' is in the back-end, so I imagine if I have properly configured my front-end (use of env variables etc.), Vue 2.7 should still be production-ready well into 2030? Whether it should be used up to 2030 is a different question.
I have business-legitimate and personal reasons not to upgrade to Vue 3.x. Most people upgrade because the ecosystem followed Vue 3, I only rely on Vue-CLI and my Vue 2 codebase is too large to refactor without security motivations.
This is a difficult question because most software isn't capable of being used as a detached front-end, therefore there isn't a lot of evidence available from what I've gathered on the internet about security vulnerabilities for this kind of framework, post EOL.