Data-driven subscriptions cannot be created because the credentials used to run the report are not stored, the report is using user-defined parameter values, or if a linked report, the link is no longer valid.You look and you are using a shared data source that has saved credentials. So that's not it.
You check and the report is not linked to any other report. So that's not it.
You go ahead and remove all the parameters and publish. So that's not it.
Is SSRS a liar? Dumb Microsoft goofed again right. Not so fast. This is still something you can fix. I came across something that could help. Check on the Variables section.
In the rdl file's xml there is a <Variables></Variables> section. Remove it and publish. The error will go away. You can also see it in the Report Properties.
Good luck and I hope this helped.