Node.js v18 is being deprecated. https://vercel.com/guides/serverless-function-contains-invalid-runtime-error says “While we continue to work on a solution, you should ensure your project remains on Node.js v18 (which uses a compatible build image). Node.js v18 will not be deprecated until at least 2025, and we are actively pursuing solutions to support your project on the latest Node.js version.”, so I’m guessing there is no solution after all despite this statement?
Would have been nice to know far in advance of the deprecation that there would be no solution so that there was time to work on a solution.