I'm really sorry, but I'm unable to get through to this website on the Pi 5 using ProtonVPN. I'm still getting that access denied dialog.
I'm able to get through on my work system via the corp VPN, I'm not sure why. I can see what you mean though, that website is awful even on an over-provisioned workstation.
I don't suppose you have a similar site to test against? if it's any consolation, I'm able to load up and navigate absolutely bullshit websites (in terms of bloat and performance) like ali express just fine.