Logging relates to what's done on the VPN and IPs that connect in a medium/long/permanent-term basis.
IPs needn't be logged. Obviously servers are aware of them to accept connectivity, but they aren't logged, all data is ephemeral and processed in real-time.
Regarding number of devices logged, that's fairly easily worked around. The client has to be connected to your account. That session ID can present a device count + 1 status to your account.
I'm not sure how Proton specifically does it, but as someone who works in the field, there are multiple ways to have that covered.
Perfect Privacy allows an unlimited number of devices. Up to 400 devices can be registered per account per server.
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