Here is all of the information I could find on ProtonVPN’s claims regarding their macOS kill switch. I could not find any other official correspondence from ProtonVPN on the matter.
Blog post: What is a kill switch?
A kill switch is available to all Proton VPN users on Windows, macOS, Linux, iOS and iPadOS. Newer versions of Android now have built-in kill switch feature, as explained below.
Please note that our regular kill switch feature can’t protect you if you intentionally disconnect from a VPN server. However, the feature does protect you while switching servers with Proton VPN.
In that same post, they even re-assure macOS users about one of the software limitations that affects all VPN providers, whilst completely omitting their own deficiency that is objectively far worse.
Important note: As we have reported, Apple’s macOS and iOS operating systems don’t close all existing connections when you connect to a VPN, specifically certain DNS queries from Apple services, even with the kill switch turned on. However, the kill switch will block all non-Apple connections. We’re aware of this issue, and are working towards a possible fix.
Blog post: What is a VPN kill switch and when should you use one?
Page context
ProtonVPN’s claim:
Proton VPN offers a full system-level kill switch on all platforms that we support — Windows, macOS, iOS/iPadOS, Linux, Linux CLI (and, of course, Android).
Blog post: Introducing Kill Switch for macOS VPN
The new, firewall-based Kill Switch prevents your IP address and DNS queries from being exposed in the event you are disconnected from a VPN server for any reason. When you enable Kill Switch, if you lose connection to the VPN service, the Kill Switch will block all external network traffic until it automatically re-establishes a connection to a VPN server.
Reply to reddit post complaining about server switching exposing their IP address on macOS:
when I try to swap from a US VPN server to a Netherlands VPN server while running an IP refresh every second, for a brief period my original IP appears in-between US and Netherlands IPs.Hi! Note that during the transition from one server to another, the kill switch should indeed be activated and you shouldn’t have internet access during this brief period of time that it takes the app to switch servers.
ProtonVPN deletes reddit post for using the terminology “IP leak” to describe the issue:
To clarify, our Support team removed this post because the title was spreading misinformation.
Proton VPN isn’t leaking your IP, you’re expecting the regular Kill Switch to do something which is not designed to do – namely, prevent you from connecting to the internet even if you manually disconnect from the VPN.
This doesn’t just seem like a line of documentation being incorrect. But I will let you judge for yourself.