1: OEM Smartspace
OEM Smartspace is a limited, legacy version of Smartspace which is still used by some OEMs. It can either be used in launchers, or on lock screens (or both).
Unlike Native Smartspace, it only allows a title, subtitle and sometimes a second complication, but no other information like images or lists. Only a single page is possible, with no possibility for scrolling or controls to change page like in Smartspacer's widget.
OEM Smartspace implementations are done by OEMs, and as a result they can look quite different from each other. This can also result in differences in functionality, for example on OnePlus devices OEM Smartspace on the lock screen may not appear unless there is both a Target and Complication available. In some cases, you may also find that Complications are not clickable, this unfortunately cannot be fixed by Smartspacer.
OnePlus' Implementation of OEM Smartspace on their Lock Screen / Always on Display
Google's previous implementation of OEM Smartspace on Rootless Pixel Launcher
OEM Smartspace requires Enhanced Mode, and on Android 10 - 11 it also requires root. This is due to permission requirements imposed by the system, there is no workaround.
In Smartspacer's settings, on the OEM Smartspace page, you will see a list of apps that declare themselves as OEM Smartspace compatible, with the option to enable it for each of them. Please note that them appearing on the list does not guarantee that OEM Smartspace will work (see below for more info).
Once enabled for an app, Smartspacer will start sending Targets and Complications to it immediately. If you are not seeing Targets, try rearranging them so a static target (eg. Google Keep) is at the top, although remember Targets can only display very basic information in this mode.
If OEM Smartspace is enabled for an app, but it does not appear, check the app's settings for a switch for "At a Glance" or similar, and enable it. In some cases (for example OnePlus devices on Oxygen OS 12), there may not be a switch, in which case you may need to run this command as root in a Terminal, and reboot:
setprop persist.enable.smartspace.lib 1