Looks like the old.reddit method doesn't work anymore but found a great solution if you're a ublock origin or adguard user.
copy/paste of reddit comment so blocked users can see it.
Go to your uBlock Origin / AdGuard filter settings page and add this custom filter (in uBlock Origin it's under the "My filters" tab):
reddit.com#%#//scriptlet('set-cookie-reload', 'reddit_session', '0')
This will automatically create the reddit_session cookie as described in the post above.
You have to make sure that you are using the latest uBlock Origin or AdGuard extension, because the cookie filter syntax has only been added recently to uBlock Origin. (The above filter only works with uBO version 1.53.0 or higher)
Here are some more techy details about the cookie filter:
It will create a session cookie, which will only last until the browser is closed. (This is good because see 2. and 3.)
You will not be able to log-in to reddit while the cookie is set. (Also applies to manual method in the original post)
If you want to log-in to reddit, you will have to remove or comment out the custom filter, then close and re-open your browser. Doing this will clear the session cookie and prevent your adblocker from automatically creating the fake session cookie again. You can comment out custom filters by prefixing them with an exclamation mark, e. g.: !reddit.com#%#//scriptlet('set-cookie-reload', 'reddit_session', '0')
The cookie value is set to '0', this is a limitation of the new cookie filter syntax. Can't make it empty as of now unfortunately. It works fine with the value set to '0' though.
reddit comment