When uploading a document in a SharePoint Online or On Prem (2019 version) the workflows starts before the document properties can be set. The properties is required for the workflow to work. In earlier versions of SharePoint when you upload a document, you have to set the required properties and then it finishes the process and only then the workflow starts. But in Online and 2019 I see that the workflow starts before you check in the document with the required properties. How can I 'hold' the workflow until the properties are set?
This is the default behavior in SharePoint online and SharePoint server 2019 modern experience, no prompt box when uploading files.
In all classic libraries, if we set required columns, the box will pop up and remind you to fill in the required columns, however, when we click cancel button, the document is still uploaded successfully with check out status.
Then, even if the required columns are not set, the workflow will still be triggered.
Therefore, I think we cannot enforce the workflow to start after filling in the required properties both in modern or classic experience.