I am wondering if it's possible to disable editing of a Survey123 feature layer when the edit is being done outside of the Survey123 form.
For example, a user could edit the feature layer table in ArcGIS Pro and all the logic/constraints/calculations in the form would not be active, since it's being done outside of the native Survey123 editor / web app / mobile form.
I think the answer is "no".
Also, user permissions like Admin override layer settings. As a result, some users can edit even when editing is disabled.
That said, I would encourage setting up sharing permissions in Portal for the layer.
I agree its a no. Worse we have users making QA changes in the service via webmap or Pro, then someone also does a change in the form, resubmits and wipes the other changes. You can turn off editing in a map but they can still backdoor to the service.
You can block this out by using a URL as your submission url, and enabling whitelisting. It requires a spare creator account though. https://support.esri.com/en-us/knowledge-base/how-to-limit-access-to-secured-hosted-services-or-map-...