Searching for 'Trapped' can be a bit confusing because there are quite a few books with that title. The most common one I see discussed in online spaces, especially on places like Reddit, is the science fiction novel 'Trapped' by James Alan Gardner. It's the story of a soldier stranded on a planet overrun by alien plant life. If that's the one, I bought my Kindle copy from Amazon.
If you mean the teen dystopian book by Megan DeVos, 'Trapped', that one seems to be exclusively on Amazon as an e-book too. Honestly, a lot of these single-word title books, especially from indie authors or small presses, end up being Amazon-only for digital versions. It's frustrating if you want to support a different store. Your best legal bet is to check the major retailers—Amazon, Barnes & Noble, Apple Books, Kobo—and see which version pops up with the right author name. A library search might also turn up something, but it's hit or miss for niche titles.