I'm using Python with Selenium to automate Edge.
Where can I find a list of all experimental_option 'prefs' keys for Edge as 'download.default_directory' and 'download.prompt_for_download'?
In other words, the keys of the dictionary for 'prefs' you can read about on page Capabilities and EdgeOptions.
I've tried to search at my best on the web.
You need to find them in chromium source code: https://chromium.googlesource.com/chromium/src/+/4aaa9f29d8fe5eac55b8632fa8fcb05a68d9005b/chrome/common/pref_names.cc.
For example, you can find download.default_directory and download.prompt_for_download in the file:
// String which specifies where to download files to by default.
const char kDownloadDefaultDirectory[] = "download.default_directory";
// Boolean which specifies whether we should ask the user if we should download
// a file (true) or just download it automatically.
const char kPromptForDownload[] = "download.prompt_for_download";