if the battery is struggling to crank the engine after it died, then it could be an alternator issue...

otherwise, the battery should fire the coils and injectors and the rest of the engine management just fine. The starter probably requires more than 90% of the current draw at start up.

Take the 2 minutes to pull the valve cover and look at your intake cam

Did you do this?

Started a new thread, same subject for sanitary purposes:

https://www.miataturbo.net/general-miata-chat-9/lost-all-engine-power-died-dead-still-dead-48391/