How do fixed sitemap the maximum limit issue?

A sitemap is a method of informing search engines about pages on your website that they would not otherwise find. Google Webmaster Tools has a feature that allows you to submit sitemaps.
Webmaster tools will provide a warning if you don't add redirect=false. If start-index=1&max-results=100 is omitted, the maximum number of URLs provided will always be 26. If your blogspot/blogger website has more than 100 pages and posts.
You need to add two sitemaps one having with (start-index=1&max-results=100) and 2nd with start(start-index=100&max-results=200).

How to fix robots txt sitemap maximum results limit issue?

if you have a site called 123.blogspot.com and you can do change your domain name as "www.123.blogspot.com" and more than pages according you do set max-results limit on your blogger for robots txt and add below sitemap in your blogger in robots txt results limit-
Sitemap: https://www.123.blogspot.com/atom.xml?redirect=false&start-index=1&max-results=100
Sitemap: https://www.123.blogspot.com/atom.xml?redirect=false&start-index=101&max-results=200
Sitemap: https://www.123.blogspot.com/atom.xml?redirect=false&start-index=201&max-results=300
Sitemap: https://www.123.blogspot.com/atom.xml?redirect=false&start-index=301&max-results=400
Sitemap: https://www.123.blogspot.com/atom.xml?redirect=false&start-index=401&max-results=500
Sitemap: https://www.123.blogspot.com/atom.xml?redirect=false&start-index=501&max-results=600