How some when I have VPN turned on, I cannot visit certain sites? And the moment I turn VPN off the site loads.I am on the Free plan of Proton, using US IP and have protocol set to Stealth.
A few examples I can think off is the USPS official website and Bitly link shortener (doesn’t work even when it’s clicking on a bitly shirt link to get redirected). They don’t load when I have VPN turned on but all other ensure loads just fine
Many companies want your data, even without your consent. Geolocation is valuable for them, and they can forbid you to access their site if they detect you are using a VPN, as they don’t really know where are you. Among other scenarios. Usual business for many sites. I’d suggest you try picking other servers or even countries until you pick one that is not blocked.
There’s an alarming amount of websites that block protonvpn servers due to “malicious use” which is making me think that my subscription to protonvpn was a waste. 
You might have a VPN on your browser. I forgot about the VPN on my browser when I turned on Proton. I had the same problem. Websites would not load. Once I turned the browser’s VPN off, it worked. Make sure Proton is the only VPN running. Maybe try turning off Stealth mode if my previous suggestion is irrelevant.
Proton isn’t “blocking” anything, if you have NetShield enabled it may break some sites because the sites tracking techniques prevent the page from loading if those trackers fail to load, the app or site is. For a while the Microsoft Store was blocking access when any VPN was active on a Windows computer. I had the issue for a while when using Nord and PIA and blamed them until discovering the real issue.
yup. one year later and its getting worse. I’m afraid my protonvpn is mostly useless now
That’s a lot of words for “this service is useless”
Do you have examples for this?