in order to disable Todoist from Outlook, go to Tools -> Trust center (in Outlook), access the Add-ins tab, choose to manage COM Add-ins (at the bottom of the window) and click "Go".
Here you can un-check (disable) or remove the Todoist add-in.
Also, you can directly delete it going to the Control Panel -> Add/Remove Programs and look for "Outlook Todoist".
The todoist Outlook install aborted due to inadequate security but keeps trying to load and giving a can't create pst file error. There is nothing in the trust center or Add/remove for todoist. I eliminated everything with todoist in the registry but I still get the error every time I load that a new pst file cannot be created.
how can I stop Outlook from loading?
a PST file is usually created by Outlook for each email account you add and it stores all your emails in such files. Are you sure that the error message is related to the Todoist for Outlook plugin?
You could try to re-install the plugin again and see if it says that "the latest version is already installed" if it returns a different error, please post the exact error message here.
Also, please use your system's Search function and look for OutlookTodoist and if any files/folders will be found, you can delete them and see if it solves this issue.