I’ve found a solution that doesn’t require enabling any extra plugins, as well as finding a fix for my hair issue!
LiveLink doesn’t need any additional face tracking system as far as I can tell. There’s just an Unreal bug where its dependencies aren’t being included in builds.
The solution for the main issue requires you to be using a C++ project, and involves adding "LiveLinkAnimationCore" into the list of PublicDependencyModuleNames in the “<Project name>.Build.cs” file (which can be found in the folder “Source\<Project name>”).
If you don’t have a C++ project, you have to include another plugin that includes the correct module, such as the “Apple ARKit Face Support” or “Faceware Live Link” plugins mentioned earlier in the thread.
The fix for the hair can be used by anyone who hits the same issue, and just involves adding the following code into the list of plugins in your .uproject file.
{
"Name": "HairStrands",
"Enabled": true
},
Edit: As I mention in a later comment, Apple ARKit is now automatically enabled when adding MetaHumans for the first time, so that should be taken as the “correct” solution.