If it's not working with your VPN, try switching to the old.reddit.com subdomain. They randomly block me sometimes using ProtonVPN, but every time I use the old site, it works fine for some reason. This also prevents Reddit blocking any browser that blocks cookies.
I also have a bookmarklet you can put in your bookmarks bar to automatically convert normal reddit links into old.reddit.com ones, should this work in your case.
javascript:(function() { var currentUrl = window.location.href; var newUrl = currentUrl.replace(/^https:\/\/www\.reddit\.com/, 'https://old.reddit.com/'); window.location.href = newUrl; })();
You can also try either a 3rd-party or locally-hosted instance of libreddit, and replace the https://old.reddit.com/ link in the bookmarklet with the URL (and if self-hosted, port) of the libreddit instance you want to use.
The instance wouldn't be protected by your VPN, (if self-hosting, would need to be split-tunneled or on a different device like a Raspberry Pi not connected through your VPN) but it's easier than constantly disabling and re-enabling your VPN for your whole device.