See code below:

type Check<T> = T extends Record<string, string> ? true : false

type T1 = Check<{ id: string }> // true
type T2 = Check<Partial<{ id: string }>> // true

type T3 = Check<Record<string, string>> // true
type T4 = Check<Partial<Record<string, string>>> // false

It seems undefined that makes Partial<Record<string, string>> not satisfy Record<string, string>, but why Partial<{ id: string }> satisfies?