Edit 4/15 -- Seems I was late to the party.
Rockedge and Wizard had worked out a different method to use ProtonVPN, viewtopic.php?p=135367#p135367.
Well, my research started with an inquiry concerning BionicPup64 about which I knew OscarTalks had created Simple VPN Implementation so took a different route.
Edit 4/13 -- Well, there's a bigger problem.
I just tried the attached pet, starting it via a terminal. Terminal print-out is that it can't find libcrypto.so.1.1. It is present in /lib/x86_64-linux-gnu and another copy just in /lib. Tried substituting the same-named file from my deployment of viber to /opt. That version also isn't found. The application runs, but I'm not sure how effective it is without libcrypto.
Edit 2 4/13 -- Sorted the above. Upgraded the OpenVPN binary to Bookworm's native and added a dependency --libpkcs11-helper.so.1. Opens and seems to function. But the question below remains.
In response to puppylinuxrocks's request for instructions how to install ProtonVPN under Bionicpup64, I suggested that it might be easier to use a Puppy such as BookwormPup64 has apt and synaptic so that Proton's official instructions could be followed. Well, then I decided to test my suggestion and, unfortunately, have to 'eat my words'. Proton's instructions provides two methods, manual or after installing network-manager via apt. The former did not work at all, and apt --after installing a bunch of dependencies-- failed to install network-manager.
So I decided to figure out whether OscarTalks's Simple VPN implementation for FossaPup viewtopic.php?p=22420#p22420 could be modified for use with Bookworm64. ListDD revealed only one missing dependency: libcrypto.so.1.1. Tracked that down via pkgs.org --it offered the Debian Bullseye version-- rebuild VPN-ONOFF with it included and it seems to be functional. However, I not sure as I don't fully understand the recipe for using it. Repeating where I left off in response to puppylinuxrock's inquiry:
I just found my notes OscarTalk's Instructions at https://oldforum.puppylinux.com/viewtop ... ad#1018172 hope this helps. Note, installing the VPN-ONOFF pet will create the /etc/vpn-onoff folder and the vpnpass file mentioned below.
"Took a look at ProtonVPN free version and was able to get it working.
Signed up with e-mail
Logged in to their website which gives me my dashboard.
From there I can download the .ovpn config files for each of their servers.
Place this (or several of them) in /etc/vpn-onoff with the others.
Delete the symlink vpnconfig
Right click the ProtonVPN .ovpn file and select "link"
Name the link you are creating as vpnconfig (replacing what you just deleted)
From the dashboard I also obtain the long random username and password which I have to use.
Those I paste into my vpnpass file (also in /etc/vpn-onoff)
I add the path to my vpnpass file into the .ovpn config file:- > Not sure what this means 
auth-user-pass /etc/vpn-onoff/vpnpass
Save and close everything.
The VPN-Start "button" in JWM menu then starts it and connects.
The FREE servers are only 2 in Japan, 2 in The Netherlands, and 2 in USA and they are all very busy, some showing 100% load and none lower than around 80% when I looked. I chose USA2 and it was performing reasonably well, although the first 7 days are trial period so speed may slow down after that. " > May have changed by now
... Does anyone know exactly what "I add the path to my vpnpass file into the .ovpn config file:- " means?"*
You can find the pet I built here, https://www.mediafire.com/folder/4wyy74 ... /VPN-ONOFF
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* Could be something as simple as editing .ovpn config file to include "auth-user-pass /etc/vpn-onoff/vpnpass"