Microsoft Windows search queries are also not case-sensitive. This includes query keywords (SELECT is identical to Select, select, and SELect) and search terms. If an identifier or literal uses Unicode characters that have case-sensitive semantics, the search engine considers all cases to be equivalent. Adding a canonical link element Rel%3D also helps confirm this and encourages search engines to focus on that version.
If you use capital letters in your URLs and someone searches for the same title with the same capital letters, there's a good chance that your URL will be displayed. Google's search engine treats search queries as case-insensitive and interprets requests in lower case. You can tell Google which version of a URL you want to appear in search results by linking to that same version in a consistent way. It doesn't matter if you search for the keyword in upper or lower case letters, the search engine will give you the same results.
If the web server does not manage case-sensitive URLs, it can direct the URL to the original URL using canonical tags and, therefore, direct the search engine to where the original content is located. Google plans to introduce “case-sensitive” search in the near future to solve this problem and be able to interpret searches in the correct context. This topic is addressed in the latest installment of Ask Googlebot on the Google Search Central YouTube channel. For example, if someone searches for “Apple” and you use the keyword “apple”, the search engine will continue to show your ad.
That's why, no matter what case you use in your keyword, you'll still get the same search results. When Google recognizes that there are several versions of the same URL, it will try to crawl them all and figure out which one to show in the search results. Since Google is the most important search engine, it's best to focus on the keywords that you use in the content of your website. Mueller answers the question and, at the same time, explains how Google chooses which version of a URL to display in search results.