Drafts - iOS Quick Capture
Drafts has two options to capture text quickly from other apps through the iOS share sheet.
Share extension: Appears as a Drafts icon in the iOS share sheet, and when selected opens a Drafts sharing window with options to edit/adjust the text, flag assign tags or flag, save in Drafts and close, use Open to continue in Drafts, and even append/prepend to existing drafts when capturing text.
Drafts Quick Capture extension: Captures the shared text as a new draft in your inbox without further interaction; it just displays a brief success message with no sharing window.
Drafts widgets are available for both macOS and iOS in various styles and sizes.
There are similar options on macOS.