Page performance and indexing are things to look out for with any web page. The idea is to make sure the content is readily available to the user on the page itself, but that it can also be found as fast as possible with a search engine.
As of May 2021, these two aspects will be intertwined more than ever in Google search with Core Web Vitals being introduced. This means that meta-tagging and being indexed aren't the only things that'll boost your website to the top of Google search results. These distinctions are outlined in this article.
Any website can be analyzed with the new Google PageSpeed Insights tool. This tool returns diagnostics on Core Web Vitals for mobile and desktop and suggests improvements that can be made to align more closely with desired loading times, level of interactivity and level of visual stability.
It is important to remember that this new tool is not absolute. There might be suggestions made by Google that will simply not work for a webpage - sometimes, large resources simply cannot be removed. The suggestions made by Google are simply suggestions and are not compulsory for "better" indexing, only the suggestions that make sense to each individual use case should be examined.