Sitemap can be read, but has errors

I recently did some changes to my sitemap because i updated my website to support two languages but now i get an error when submitting the sitemap and i don’t see where the problem is.

Your Sitemap or Sitemap index file does not properly declare the namespace. 
>     Examples >     Line 5 >     Parent tag: >     url >     Tag: >     link        <urlset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xhtml="http://www.w3.org/TR/xhtml11/xhtml11_schema.html" xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd http://www.w3.org/TR/xhtml11/xhtml11_schema.html http://www.w3.org/2002/08/xhtml/xhtml1-strict.xsd">     <url>     <loc>https://example.com/</loc>     <xhtml:link rel="canonical" href="https://example.com/"/>     <xhtml:link rel="alternate" hreflang="el" href="https://example.com/"/>     <xhtml:link rel="alternate" hreflang="el-GR" href="https://example.com/"/>     <xhtml:link rel="alternate" hreflang="x-default" href="https://example.com/"/>     <xhtml:link rel="alternate" hreflang="en" href="https://example.com/en"/>     <lastmod>2020-02-25T12:41:35+00:00</lastmod>     <priority>1.00</priority>     </url>              ````````           </urlset> 

***Update

Tried this method like the Google Documentation says so

<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"   xmlns:xhtml="http://www.w3.org/1999/xhtml"> 

Although when using xmlns:xhtml="http://www.w3.org/1999/xhtml" converts the xml to plain text, changing http to https outputs the xml correctly and does the work but i have read you must use only http to avoid my issue, honestly this it too confusing.