How do I transfer my WhatsApp chats from Android to a new iPhone without losing them?

You're right that it doesn't 'just restore', Android backs up to Google Drive and iPhone restores from iCloud, so they don't talk to each other. The official route is Apple's 'Move to iOS' app: install it on the Android, set up the iPhone as new, and on the 'Apps & Data' step choose 'Move Data from Android'. It shows a code, connect both phones, and select WhatsApp among the data, WhatsApp prepares an export and moves the chats. Requirements: the iPhone must be new or freshly reset (this only works during setup), both phones plugged in, same number, recent app versions.

The gotcha: it only works during the iPhone's initial setup with 'Move to iOS', not after. If you already finished setting up the iPhone, you'd have to reset it (or use a paid transfer tool) to bring the chats over.