You are unlikely to be alone in your preference.
Apple doesn't offer hard-copy User Guides - presumably, due to the constant introduction of new features, any hard-copy Guide would be significantly out-of-date very quickly. Apple does, however, provide User Guides that can be accessed online. Clearly, unlike a downloadable version, online Guides are inaccessible if you don't have access to an internet connection at the time of need.
For reasons known only to Apple, downloadable (PDF) versions of the iPad and iPhone User Guides have not been released for iOS/iPadOS 17/18 - but are available for iOS/iPadOS 13-16.
For iOS/iPadOS 17/18, the associated User Guides are only available as on-line web pages. The Tips App, installed by default on all recent models of iPad, provides a brief introduction to the main features of your device - and leads you to the User Guide. In case you missed it, here is a link to the Tips App:
https://apps.apple.com/gb/app/tips/id1069509450
For earlier versions that do have an downloadable version of the User Guides, these are accessed using the Apple Books App. If not already installed on your devices, the Books App can be installed from the Apple App Store:
https://apps.apple.com/app/apple-books/id364709193
Apple does invite submission of comments and feature requests via its Product Feedback portal. If you would like Apple to reconsider publishing their User Guides as a downloadable PDF, this would be the most appropriate channel through which to make your request:
Feedback - Apple