Taildrop not showing any devices

I’m using Tailscale 1.40.0 (MAS version) on macOS 12, and I cannot see any other devices when using the Taildrop share window:

Easily send files to your own devices on a Tailscale network from here. Get started by installing Tailscale (v1.8 or later) on another device and sign in to the same network. It will appear here.

Nothing appears in the window. Clearly there are other devices online:

One of them (to which I want to share) is running Tailscale 1.40.0 under Windows 10.

Both devices are logged in and have Internet connectivity.

Any ideas on what I could try?