That may be because my copy of Devonthink has never asked.
Actually, if you every ran the Script > Reminders > Add as To Do to Reminders, you would have been asked.
If you denied access, Apple has not given you a way to undo that choice.
In fact, the only option you may find involves a Terminal command and that still will likely not work. (I’ve never gotten it to accept a second choice myself.)
I have a similar issue. DT3 asked for permission for Reminders access and I accepted butI got the above mentioned error dialog box. For Calendar everything is working normally. DT3 is in the list of Calendars but not in Reminders of the Privacy tab in System Preferences. I reset the privacy using the terminal command “tccutil reset Reminders” but did not solve the problem