This simplifies the process of loading custom fonts that are resources in an iOS Apple SPM Package (Swift Package Manager).

Font+Autoregistering.swift

import Foundation
import UIKit

public typealias FontNameExt = (name: String, ext: String)

public func autoRegisteringFont(_ fontNames: [FontNameExt], _ spmBundleName : String) throws {
  guard let spmBundle = Bundle(bundleName: spmBundleName) else {
    throw("Fail to find bundle(\(spmBundleName).bundle) in your app bundle.")
  }
  try fontURLs(for: fontNames, in: spmBundle).forEach { try registerFont(from: $0) }
}

extension Bundle {
  convenience init?(bundleName: String) {
    self.init(path: "\(Bundle.main.bundlePath)/\(bundleName).bundle")
  }
}

func fontURLs(for fontNames: [FontNameExt], in bundle: Bundle) -> [URL] {
  return fontNames.compactMap { police in
    bundle.url(forResource: police.name, withExtension: police.ext)
  }
}

func registerFont(from url: URL) throws {
  guard let fontDataProvider = CGDataProvider(url: url as CFURL) else {
    throw("Could not get reference to font data provider.")
  }
  guard let font = CGFont(fontDataProvider) else {
    throw("Could not get font from CoreGraphics.")
  }
  var error: Unmanaged<CFError>?
  guard CTFontManagerRegisterGraphicsFont(font, &error) else {
    throw("Error registering font: \(dump(error)!).")
  }
}

Didn't get that.
I'm using this in SPM and made public func to register fonts in SPM. Calling that public func method from app's didFinishLaunchingWithOptions and working like charm.
I think SPM is the module itself. Are you having multiple Modules in a single SPM?

Take a look at Access a Resource in Code

Yes 126 SPM modules that means 126 library targets all in the same Package.swift