Matthew Cassinelli put together this fantastic guide for quick capture in Ulysses on iOS. He goes over the built-in share sheet (which is what I use about 5 times a day). And he also gives several examples of custom Shortcuts (with download links) for automating the capture of ideas, notes, and more.
Side note: On this Tuesday 26 March, we are shipping a huge update our Learn Ulysses course over on The Sweet Setup. This article on Quick Capture is taken from one of the lessons in the new course.