A few minutes, once.
Download Spooky.pkg and open it. It installs Spooky in Applications and Spooky Microphone, which lets the Mac use your iPad's microphone. The installer is signed and notarized by Apple.
Spooky lives in the menu bar, as a small ghost. The first time, it asks for two macOS permissions: Screen Recording, to show the Mac's screen on your iPad, and Accessibility, to move the pointer and type from your iPad. macOS asks you to confirm them in System Settings; Spooky notices by itself when they are on.
The app is coming soon to the App Store.
On the Mac, choose Pair a Device… in Spooky's menu and scan the code with the app. If the Mac and the iPad use the same Apple Account, the Mac also shows up by itself through iCloud.
Install Tailscale on the Mac and on the iPad or iPhone, signed in with the same account. Spooky then reaches your Mac from anywhere.
Apple devices share a direct Wi-Fi link (used by AirDrop and Cursor and Keyboard) that can briefly take the iPad away from your home network. If the stream stutters at regular intervals: