not possible to exclude sitemap from "main" sitemap while including it in robots.txt

[Sammeeey]

Describe the bug
I have this in my sitemap.xml (when using robotsTxtOptions.additionalSitemaps):

<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <sitemap>
    <loc>https://www.domain.com/sitemap-0.xml</loc>
  </sitemap>
  <sitemap>
    <loc>https://www.domain.com/server-sitemap-index.xml</loc>
  </sitemap>
  <sitemap>
</sitemapindex>

When I want this:

<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <sitemap>
    <loc>https://www.domain.com/sitemap-0.xml</loc>
  </sitemap>
</sitemapindex>

To Reproduce

1. create server-sitemap-index.xml/route.ts to generate server-sitemap

2. next-sitemap.config.js:

/** @type {import('next-sitemap').IConfig} */
const siteUrl = process.env.NEXT_PUBLIC_SITE_URL
module.exports = {
  siteUrl: siteUrl,
  sitemapSize: 50000,
  generateRobotsTxt: true,
  exclude: ['/server-sitemap-index.xml', '/sitemap/*'],
  robotsTxtOptions: {
    additionalSitemaps: [
      `${siteUrl}/server-sitemap-index.xml`,
    ],
  },
  transform: async (config, path) => {

    return {
      loc: path,
    }
  }
}

But robots.txt should include the server-sitemap-index.xml:

# *
User-agent: *
Allow: /

# Host
Host: https://www.domain.com

# Sitemaps
Sitemap: https://www.domain.com/sitemap.xml
Sitemap: https://www.domain.com/server-sitemap-index.xml

Expected behavior
robotsTxtOptions.additionalSitemaps shouldn't add the sitemap to sitemap.xml BUT only to robots.txt

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Additional context
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