How to combine a regular static sitemap index with a server sitemap index

[ghost]

Currently, my website is organized as follows:

/sitemap.xml (static index)

<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<sitemap><loc>https://example.com/sitemap-0.xml</loc></sitemap>
<sitemap><loc>https://example.com/server-sitemap.xml</loc></sitemap>
</sitemapindex>

/server-sitemap.xml (server index)

<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<sitemap><loc>https://example.com/server-sitemap/users-0.xml</loc></sitemap>
</sitemapindex>

As you can see above, it is a nested index, SearchConsole has an error, and the sitemap is not recognized.

What can I do to improve these?
I feel like it would be nice if I simply didn't include server-sitemap.xml in sitemap.xml, but I want to put it all together in a single sitemap.
Can sitemap.xml contain the contents of server-sitemap.xml?