Hello,
I am the Esri analyst working with Veronica and just wanted to drop in to share a bit of our discussion to a larger audience of Leica users.
From my understanding, it seems that the units are no longer able to login to ArcGIS Online after the TLS 1.2 update. However, Collector itself does have other options. For example, users using Collector to log in to Portal for ArcGIS (as part of an ArcGIS Enterprise deployment) should not be affected as the connection is now between the GPS unit and your Portal for ArcGIS Deployment as opposed to a connection between the unit and ArcGIS Online.
Choosing between ArcGIS Online and Portal for ArcGIS
https://enterprise.arcgis.com/en/portal/10.6/administer/windows/choosing-between-an-arcgis-online-su...
Portal for ArcGIS (as part of an ArcGIS Enterprise Deployment) understandably does require more active maintenance as opposed to ArcGIS Online but the option is there as a workaround for the existing issues connecting to ArcGIS Online. We also offer Esri Managed Cloud Services should you want to avoid actively managing the environment within your organization. Esri also provides Amazon Machine Images (AMIs) within the AWS Marketplace which would allow you to setup an ArcGIS Enterprise deployment as well.
Esri Managed Cloud Services
https://www.esri.com/en-us/arcgis/services/managed-cloud
Esri and AWS
https://aws.amazon.com/solutions/global-solution-providers/esri/
Base ArcGIS Enterprise deployment
http://enterprise.arcgis.com/en/get-started/latest/windows/base-arcgis-enterprise-deployment.htm
I would recommend that customers who are experiencing these issues should reach out to their Account Manager here at Esri to discuss the issues you are experiencing as well as potential solutions we can offer which may or may not be one of the ones listed above (licenses, onsite engagements from Esri, etc). A proxy may also be a solution, but that would be more of a conversation to be had with our consultation services here at Esri and/or a customer's IT department as to the feasibility of a proxy.
Thanks!
Travis