You can import worlds and resource packs in iOS 13 and above by using the Files app and the Notes app.
- Download the world/pack.
- Open the Files app and navigate to the "Downloads" folder.
- Press and hold on the pack or world to bring up a menu, then select "copy."
- Open the Notes app and create a new note.
- Tap in the note to bring up the edit menu, then select "paste." The file link will be pasted into the note.
- Tap on the file to bring up a screen showing an icon, the file size, number of files, and "Preview Content" button.
- In the lower left corner of the screen, tap the the "share" icon.
- Select Minecraft from the list of apps in the bottom row of the share options.
Once you see the "import successful" message in Minecraft, you can safely delete the world/packs from Notes and Downloads, because Minecraft copies the files to the appropriate game folder when it imports them.