To create a URL you can set a text type state being “This URL”?parameter=value or just write it https://yourapp.com/yourpage?parameter=value
Like:
https://yourapp.com/yourpage?shared=yes&title=title-of-the-post-you-created
Then give that text to your user so he feeds whoever he wants with it.
Then to grab it when a user lands on the page through the shared link:
Event: Page is loaded, with a condition to this event being “Get data from page URL” parameter => shared = yes | So this workflow will only trigger if it’s a shared link.
Then you can use action “Display data in a popup: Do a search for Posts, criteria is post title = Get data from page URL parameter => title”.
Click here for Bubble’s reference on this.
Also there’s this discussion (among many others) around URL parameters.
Let me know if this helps.