IIRC it’s missing a number of features that ProtonVPN Windows has. I last checked into it a year or so ago and the attitude was that it was a very shoddy application missing most features. I found this github issue expressing this sentiment but I don’t see much in terms of specifics.
I don’t have a paid ProtonVPN but I just downloaded the VPN on a free account and it only has 3 options on it:
Secure Core on/off (only select servers in privacy-friendly countries)
Netshield (DNS adblocking etc)
Killswitch
I use Mullvad so I opened that up alongside and will list out the features it has on its Linux client in comparison:
The main ones for me are split tunneling and Wireguard. Using a VPN that doesn’t support these is a non-starter for me, unfortunately. If any of this is different when you have a paid ProtonVPN account let me know - I don’t have very much experience with it.
TBH, if protonVPN under linux was any good I would probably have Proton Unlimited. I can’t justify paying for Mullvad and Proton Unlimited, so I DIY my own collection of services to match functionality for about the same price.