Element implicitly has an 'any' type because expression of type 'string' can't be used to index type

Bug Report

The following code used to work on 4.2.3, but does not build with 4.3.2, reporting the error on the last line

type ObjectFixedKeys<T extends object> = {
    [K in keyof T]: string extends K ? never : K
} extends { [_ in keyof T]: infer U }
    ? U
    : never

type DistributeKeysUnion<U> = U extends string
    ? { [K in U]: any }
    : never

type ObjectDictionaryKeys<T extends object> = Exclude<
    T,
    DistributeKeysUnion<ObjectFixedKeys<T>>
    >

type Condition = { $and: Array<Condition> }
    | { $or: Array<Condition> }
    | { [member: string]: string }

type O = ObjectFixedKeys<Condition>
type D = DistributeKeysUnion<ObjectFixedKeys<Condition>>

declare const s: string
type CT = ObjectDictionaryKeys<Condition>
declare const ct : CT
const h = ct[s]

Error:

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'CT'.
  No index signature with a parameter of type 'string' was found on type 'CT'.

🕗 Version & Regression Information

I tracked the regression to the version 4.3.0-dev.20210422

Probably related to https://github.com/microsoft/TypeScript/commit/8ea4ec94967c9db8542ca229dedd656fe9e051df

⏯ Playground Link

Playground link with relevant code

Note how the last line is evaluated to never, however if you select version 4.2.3 it gets evaluated to "foo" | "bar" as expected.