How to exclude RealityKitContent from Swift package for iOS?

I've created an app for visionOS that uses a custom package that includes RealityKitContent as well (as a sub-package). I now want to turn this app into a multi-platform app that also supports iOS.

When I try to compile the app for this platform, I get this error message:

Building for 'iphoneos', but realitytool only supports [xros, xrsimulator]

Thus, I want to exclude the RealityKitContent from my package for iOS, but I don't really know how. The Apple docs are pretty complicated, and ChatGPT did only give me solutions that did not work at all.

I also tried to post this on the Swift forum, but no-one could help me there either - so I am trying my luck here.

Here is my Package.swift file:

// swift-tools-version: 5.10

import PackageDescription

let package = Package(
    name: "Overlays",
    platforms: [
        .iOS(.v17), .visionOS(.v1)
    ],
    products: [
        .library(
            name: "Overlays",
            targets: ["Overlays"]),
    ],
    dependencies: [
        .package(
            path: "../BackendServices"
        ),
        .package(
            path: "../MeteorDDP"
        ),
        .package(
            path: "Packages/OverlaysRealityKitContent"
        ),
    ],
    targets: [
        .target(
            name: "Overlays",
            dependencies: ["BackendServices", "MeteorDDP", "OverlaysRealityKitContent"]
        ),
        .testTarget(
            name: "OverlaysTests",
            dependencies: ["Overlays"]),
    ]
)

Based on a recommendation in the Swift forum, I also tried this:

    dependencies: [
         ...
        .package(
            name: "OverlaysRealityKitContent",
            path: "Packages/OverlaysRealityKitContent"
        ),
    ],
    targets: [
        .target(
            name: "Overlays",
            dependencies: [
                "BackendServices", "MeteorDDP",
                .product(name: "OverlaysRealityKitContent", package: "OverlaysRealityKitContent", condition: .when(platforms: [.visionOS]))
            ]
        ),
       ...
    ]

but this won't work either.

The problem seems to be that the package is listed under dependencies, which makes the realitytool kick in. Is there a way to avoid this? I definitely need the RealityKitContent package being part of the Overlay package, since the latter depends on the content (on visionOS). And I would not want to split the package up in two parts (one for iOS and one for visionOS), if possible.