I have a service (made using the Shortcuts app) that takes whatever I've highlighted and pipes it to ChatGPT with a prompt that basically says "the user, who is a reasonably educated software developer, wants you to explain/analyze/summarize this piece of text that they've highlighted", and shows the result in a pop-up window.

What's amazing is that I could've built the shortcut on my iPhone while commuting to work, it's all built right in. The same service works without a single change on iPhone, iPad and Mac (where it's possible to assign a keyboard shortcut to it).