We have a Enterprise login problem for ArcGIS Online accounts on Collector (v20.1) and now Explorer (also 20.1) on Android 9 devices.
It is throwing up the "The server you are trying to connect to (https://www.arcgis.com) cannot be verified" error after entering the url and selecting the organization's Enterprise login name. It also gives a similar error on Survey123 v3.9.148, but this asks if you wish to continue, whereas Explorer and Collector do not.
I am aware that there have been similar certificate issues flagged previously for more recent versions of Collector - see posts here and here - but we have tried installing certs locally on the device, as suggested, to no effect. These posts also refer to Portal, whereas we are only trying to access ArcGIS Online at this time. It is possible to login to ArcGIS Online within the device's internet browser with no such issue. As you would expect, there is a reluctance to upgrade the Survey123 version further in case it ends up with the same problem.
Thanks for any insight.