Sorry for the late reply! Busy part of the year!
@JimmyKater The one provided through my link is a newer build. In the future I will definitely do such thing as it is very much confusing. Yes. You do need to remove the old version before installing the new one.
@HTGuru The 1.0 build was not available for free use; as off 2.0 it is. Internally though I started over with the version numbering as 1.0. As I changed from how the dialogs are displayed and other major changes.
Regarding to your issue; Does your server support TLS 1.2 (enforce), any (external) firewall involved? You may send me a PM if you want to share more information regarding to your setup, ill happily look with you into it there. Same goes from @Ghizmo_MTP. Unfortunately I don’t know the default configuration for the nextcloud-vm.
Usually though these kind of errors are related to the certificate, a good indicator to check if your Nextcloud installation works as expected is to use Internet Explorer (especially in the case of a self-signed certificate) and try a service as https://www.ssllabs.com/ to check out your https connection.
To clarify throughout the forum topic:
The language bug was fixed. Also for the free edition in HKCU/Software/NextcloudOutlookFE keys are made, for the enterprise its HKCU/Software/NextcloudOutlook. Hopefully this clarifies things.