I don't get why they say that? Sure, maybe the attackers don't know that I'm on Ubuntu 21.2 but if they come across https://paperless.myproxy.com and the Paperless-NGX website opens, I'm pretty sure they know they just visited a Paperless install and can try the exploits they know.
Yes, the last part was a bit snarky, but I am truly curious how it can help? Since I've looked at proxies multiple times to use it for my selfhosted stuff but I never saw really practical examples of what to do and how to set it up to add an safety/security layer so I always fall back to my VPN and leave it at that.