@privacyguides
They updated the part about macOS

"Important note: On macOS, the regular kill switch has two known limitations. When switching servers, there’s a brief period where your real IP address may be temporarily exposed. We’re working on fixing this. ..."

https://protonvpn.com/support/what-is-kill-switch

@privacyguides I don't know exactly where you got Proton's claim from ... but this is what they say in their support section:

A kill switch is a security feature that protects your IP address in case you unexpectedly lose the connection to a Proton VPN server. In case the connection is interrupted, a kill switch blocks all external network traffic to and from your device *until the connection is automatically re-established to the same VPN server. *

(my highlight)
source: https://protonvpn.com/support/what-is-kill-switch

This is generally how kill switch works basically everywhere. As it doesn't tear down the virtual network interface (including the redirect routes, routing your internet traffic via the VPN) until it has established a new connection to the remote server.

What is being demonstrated here is that the user implicitly disconnects the connection before starting to connect to the new chosen server.

A more accurate test for kill switch is to block the network traffic for the amount of time it takes for the VPN client to start "recovering" the connection by establishing a new connection to the same server. That new server may have a different IP address.

The reason this isn't possible to achieve when switching servers completely is that the encryption certificates would result in a mismatch, thus tearing down the connection as the client wouldn't be able to identify if it's a man-in-the-middle (MITM) attack happening, with a host trying to impersonate the real VPN server it should be connected to.