How to use multiple displays ?
There is no limit in Millumin about displays, the only limit is the hardware : in brief, how many displays you can physically connect to your computer.
It is recommended to use active adapters to connect your displays. For a better understanding about active VS passive adapters, you can watch this video.
If you want to get more outputs than your computer can offer, please read the sections below.
A splitter is recognized by your system as a giant display, then it splits this big resolution into smaller outputs.
There are several cards on the market, but the Datapath FX4 is probably one of the best. It can split a big 4K HDMI/DisplayPort output into 4 smaller 1080p60 HDMI/SDI outputs. Please note that multiple FX4 can be synchronized together, see this article : How to synchronize multiple Datapath Fx4 ?
Years ago, the Matrox TripleHead was quite popular, but it tends not to work properly on recent computers. If you are using this card, be sure to check this compatibility sheat.
These are special device supported by Millumin, that can output to HDMI or SDI.
For example, the Ultrastudio Monitor 3G can output to 1080p60 HDMI/SDI. The Blackmagic Decklink 8K Pro is quite affordable and can manage up to 4 x 4K SDI outputs : with splitters, it means that you can manage 16 x 1080p60 outputs.
You can even embed such cards inside a Thunderbolt chassis, but keep in mind that Thunderbolt bandwidth will limit the outputs to 2 x 2160p60 (or equivalent).
This is a technology that creates a virtual display on your computer, then sends its content to a compatible device. This requires to install drivers.
For example, the Startech USB to VGA Adapter connects via USB and can output 1920x1200. The Plugable USB-C Triple HDMI Display Docking Station connects via USB-C and supports 3 HDMI outputs.
However, from experience, frame drops can arise (this may be fixed in later DisplayLink update).
These are not splitters, it just provides more DisplayPort or HDMI ports via USB-C or Thunderbolt. Consequently, if your graphic card has a limitation in terms of numbers of outputs (such as for Apple Silicon computers), this will not help you to get more outputs.
Example of such docks is the CalDigit Mini Dock, that provides 2 HDMI outputs via Thunderbolt 3.
Also, eGPU can be a good alternative to get multiple outputs. However, they only works on with Intel computers, not with Apple Silicon ones.
More info in this article : Can Millumin use an eGPU ?
Lastly, you could use multiples machines all synchronized via a timecode.
See this article more more info : Timecodes