Encountered this and I know I'll end up making the same mistake again. Saving it here so I can hopefully find it on Bing ™️ in the future.
Argument of type 'VueConstructor<Vue>' is not assignable to parameter of type 'FunctionalComponentOptions<Record<string, any>, PropsDefinition<Record<string, any>>>'.
Property 'functional' is missing in type 'VueConstructor<Vue>' but required in type 'FunctionalComponentOptions<Record<string, any>, PropsDefinition<Record<string, any>>>'.