Vaaky Highlighter is a free, easy-to-use, syntax highlighting tool for WordPress. Highlighting is powered by the Highlight.js javaScript syntax highlighter with language auto-detection and zero dependencies.
Using it will be as straightforward as adding a replacement Vaaky Highlighter Sourcecode block (Gutenberg) and insert the code that you wish to highlight: Vaaky Highlighter takes care of the rest!
Here is the demo page of all the supported themes.