How to make an imported object completely immutable even when passed down to a class? [duplicate]

I have a module defaultSettingsDefs which defines and exports an object defaultSettings:

/* defaultSettingsDefs.js */

const defaultSettings = {
    theme: 'light',
}

export { defaultSettings }

And I have a class Settings (which handles app settings' changes) which is fed defaultSettings in the constructor like so:

/* index.js */

import { Settings } from './classes/Settings'

import { defaultSettings } from './defs/defaultSettingsDefs'

const settings = new Settings(defaultSettings)

Since defaultSettings is imported from defaultSettingsDefs also in many other places within the app, I tried to make it completely immutable in order to avoid accidental overwrites. So in order to take care of the properties I froze the object within the definition itself:

/* defaultSettingsDefs.js */

const defaultSettings = Object.freeze({
    theme: 'light',
})

export { defaultSettings }

which works fine and doesn't allow overwriting defaultSettings's properties neither from index.js nor, for example, from Settings itself;

Furthermore, overwriting defaultSettings itself (not its properties) from index.js correctly throws an error as expected and desired, since defaultSettings is a module import:

import { Settings } from './classes/Settings'

import { defaultSettings } from './defs/defaultSettingsDefs'

defaultSettings = 1

// throws "Uncaught TypeError: Cannot set property defaultSettings of #<Object> which has only a getter"

however, defaultSettings itself can still be overwritten, e.g., from Settings in the constructor:

/* Settings.js */

constructor(defaultSettings) {
    defaultSettings = 1
}

// doesn't throw any error and messes up my app

First off, I don't quite understand why this happens. Shouldn't defaultSettings's immutability persist when it's passed down to a class?

And secondly, how do I go about fixing this?

Thanks a lot!