Don't use noindex, it's just not necessary. It seems you have a XSL/XSLT for the sitemap, which doesn't help and is the most likely cause for Google adding the sitemaps in its' index by mistake.
EDIT: Unless you specifically restrict indexing of your sitemaps, Google will archive them in its' index. However, if you have followed the rules and guidelines, it will be hidden from most SERPs unless specifically searched for. Also, this from Google
Using a sitemap doesn't guarantee that all the items in your sitemap will be crawled and indexed, as Google processes rely on complex algorithms to schedule crawling. However, in most cases, your site will benefit from having a sitemap, and you'll never be penalized for having one.
Remove the timestamps from your robots.txt. See below for example. More about robots
Sitemap: https://milyin.com/sitemap.xml Sitemap: https://milyin.com/sitemap-home.xml Sitemap: https://milyin.com/sitemap-posttype-post.2019.xml
... and so on.
Afterwards, submit it as your sitemap-index in GSC.