This is in my opinion the simplest and easiest to make forced reset trigger.
It is a single component that can be installed in standard AR15s with no permanent modifications. It replaces the standard disconnector with a single camming surface that kicks the trigger forward as that hammer comes back. It is incapable of any mode of firing other than forced reset.
This is optimally suited for laser cutting or die blanking using steel or aluminum material. This part could cost pennies to manufacture if appropriate tooling was available. I don't think this is suitable for plastic for more than a few rounds.
This is something I was messing around with back in the Fall of 2019. I originally intended to make a commercial venture out of it but then realized I didn't have the resources to deal with seeking a classification from the ATF. Since then these files have sat on my hard drive, I no longer have any interest in this project and am now releasing the files for anyone to use for their own purposes. The farthest I got in development was design and I never got to test it out so it may or may not work. Your mileage may vary.