Internet Explorer 11 has an integrated Adobe Flash Player plugin, but on Windows Server 2016, this plugin is not active by default. In fact, checking the available plugins within IE does not show the plugin as installed. This is because the plugin is not activated by default (which is somewhat logic as it's considered a security risk).
The package containing the plugin does exist on Windows Server 2016 (with GUI) but is not active. You can manually activate the plugin through dism:
Windows Server 2016 no longer has an option to enable Desktop Experience from Server Manager. Instead, most (but not all) features are enabled by default. One such feature is Windows Photo Viewer, which no longer seems to be available, and there's no clear way of enabling or installing it. Luckily, there's a workaround to get it enabled again.
First of, you need to check on Server 2016 whether the required files are already present. If you have selected to install the full UI, the required files should already be there:
C:\Program Files\Windows Photo Viewer\
C:\Program Files (x86)\Windows Photo Viewer\
They should already be present on a fresh install of Server 2016, but if not, then you ...