I think the code needs to be updated. 2019.4, they made changes.

[LanceJZ]

Assets\Scripts\ECS\Systems\TimedDestroySystem.cs(12,26): error CS0115: 'TimedDestroySystem.OnCreateManager()': no suitable method found to override
It looks like it is using obsolete code. IE: IJobForEachWithEntity

[InnerScript]

There is a bunch of obsolete code for 2019.x and 2020.1... It would be nice to have this demo to reference with the latest changes

[tuunit]

You you want a working version you can check out my fork. But a lot has changed since this presentation therefore this repository might not be your best bet as a reference anymore.
https://github.com/tuunit/AngryBots_ECS

[humbertovirtudes]

check out my fork for a version updated to Unity 2020.3

https://github.com/humbertovirtudes/AngryBots_ECS_2021.3