How to solve the problem that Sitemap is submitted successfully but not indexed by Google?

Server Problems: If you are having problems with your server, it may cause Google to be unable to access your website. This can be caused by a server crash, overload or downtime. If you suspect a server problem, contact your hosting provider to resolve the issue.
Website Structure Problems: If your website is poorly structured, it may result in Google not being able to index your website correctly. This can be caused by your site’s unclear structure, duplicate pages, missing key information, etc. To address these issues, you may consider redesigning your site structure and ensuring that each page has a unique title and description.
Content issues: If your website content is not of high quality, it may cause Google to be reluctant to index your website. This can be caused by your content not being detailed, useful or original enough. To address these issues, you may want to consider increasing the quality of your content and ensuring that your content is original.
Competition issues: If your website is in a competitive industry, it may cause Google to be reluctant to index your site. This could be due to your competitors having built a stronger online presence or they have built more links in the search engines. To address these issues, you may want to consider improving your online presence and increasing the number of links you have.
If your sitemap has been successfully submitted but Google is not indexing your site, you may want to consider taking the following steps:

Check your Sitemap: Ensure that all pages are included in your Sitemap and that there are no errors. You can use the Sitemap report in Google Search Console to check if there are any problems with your Sitemap.
Improve the quality of your website: Make sure your website is of high quality and provides useful information. You may want to consider increasing your content, making sure your site is well structured, and making sure your site is fast.
Build more links: Increasing the number of links you have can help your website to be found more easily in search engines. You can consider exchanging links with other websites or using social media to increase your link count.
Use Google Search Console: Use Google Search Console to monitor the indexing of your website and look for any problems. You can use the tools in Google Search Console to resolve any issues and ensure that your site is indexed correctly.
For example, let’s say you are the owner of a cross-border e-commerce site and you have submitted your sitemap to Google, but Google is not indexing your site. You may consider checking your Sitemap to make sure it doesn’t have any errors and contains all the pages. You may also want to consider increasing your content to ensure that your site is high quality and provides useful information. You can use social media to increase the number of links you have and use Google Search Console to monitor your site’s indexing. If you still can’t solve the problem, you may want to consider exchanging links with other cross-border e-commerce sites or seeking professional SEO help.

Creating and submitting sitemaps
Google supports sitemap formats defined by the sitemap protocol. Each sitemap has its own strengths and weaknesses; choose the sitemap format that best suits your site and settings (Google has no preferences).

Site Map Best Practices
Site map best practices are defined by the Site Map Protocol. The most overlooked best practices are related to size limits, sitemap location, and URLs included in the sitemap.

Site Map Size Limits: Regardless of format, a single site map must not exceed 50MB in file size (uncompressed) and must not contain more than 50,000 URLs, or the site map must be split into smaller site maps. You can also choose to create a sitemap index file and submit this index file to Google; you can submit multiple sitemaps and sitemap index files to Google. This may be useful if you want to track the search results of individual sitemaps in the Search Console.

Site Map File Encoding and Location: Site map files must be UTF-8 encoded. You can host the sitemap anywhere on the site, but unless you submit the sitemap through the Search Console, the sitemap will only affect the directories below it in the parent directory. Therefore, if the sitemap is published in the root directory of the site, it can affect all files on the site, so we recommend publishing the sitemap in this directory.

Attributes of referenced URLs: Please use fully qualified absolute URLs in your sitemap; Google will crawl strictly on the URLs you list. For example, if the site is located at https://www.guangweiblog.com/, instead of specifying a URL such as /mypage.html (a relative URL), use the full absolute URL: https://www.guangweiblog.com/mypage.html.

Add the URLs you want to see in Google’s search results to the sitemap.Google usually displays canonical URLs in its search results, which you can influence through the sitemap. If you have different URLs for the mobile and desktop versions of a web page, it is recommended that you point to only one version in the sitemap. However, if you feel you need to point to both, add a note to the URL indicating which is the desktop version and which is the mobile version.