Here’s ProtonVPN’s response, dated Nov. 2, 2022, regarding some sites blocking access when P.VPN is enabled:
Thank you for contacting us.
Kindly note that some websites/services are actively blocking known VPN IP addresses. Furthermore, please note that some websites/services are not VPN friendly and are actively blocking VPN-related IPs as part of some security policies/measures they have implemented internally, and usually, they don’t tend to make any exceptions.
However, since different servers have different IP addresses, feel free to try most of our servers in order to test if you will be able to access the content with some of them.
In the process, please clear your browser cache, or access the website via an incognito/private window which should clear everything for the current session.
If you are unable to access the content with any Proton VPN server, that means that our servers are blocked, unfortunately.
Additionally, kindly note that there is a restriction on the Truth Social website, and because of that restriction only people in the US are able to use the service.