In [Typescript 3.7](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#the-usedefineforclassfields-flag-and-the-declare-property-modifier) the `declare` keyword was added as a property modifier to specify that an inherited class property should have no initializer. Seems like something in Typescript 4.3 made the change breaking, and now these fields must be either initialized or prefixed with the `declare` keyword.