The second parameter initialSize of useContainerQuery must be defined in a typescript project, even though it is optional.

To fix this, all that needs to change ia this line:

export const useContainerQuery = (query: Query, initialSize: Size) => {

https://github.com/react-container-query/react-container-query/blob/master/src/index.tsx#L15

to:

export const useContainerQuery = (query: Query, initialSize?: Size) => {