By default, any application's memory can be read and written to by other processes running as the same user, as far as I know. The way to deal with this is to set process security descriptors, but admin can still bypass this. There are protected processes, and protected processes light, but those are not used by most software (mainly anti-malware afaik.)
Although that was definitely the intent, I actually don't know about specific things that use it. I'd love to hear what actually uses it. (I don't think Widevine l3 does, for example.)
https://learn.microsoft.com/en-us/windows/win32/procthread/p...