DIY Underground Bunkers/Shelters.....

A few immediate thoughts, based on the first video only and preview of the other parts of the video (which I understand you must pay for):

1/. Extremely poor quality footing

Not only are the beams undersized, but they lack sufficient reinforcement.  They will lack ductility and strength.  They are not designed to support the lateral (sideways) soil loading either.

The slab also does not appear to have reinforcement mesh, meaning it will likely crack and not perform as desired.

It also lacks a vapour membrane and quarry rubble bedding, meaning moisture will rise through the slab, causing it to fret (pieces to fall off) over time.

During the concrete placement, it does not look like the concrete was properly vibrated, meaning you will end up with a very porous and poor quality product.

2/. No reinforcement and core fill to the masonry

This is a unbelievably bad idea.  For the soil retained, I would expect a series of vertical bars to transfer the load to the slab/roof diaphragm (and then to shear walls).  Not placing these reinforcement can lead to failure, which will be very expensive.  Even worse, without reinforcement, you have just increased the risk of sudden catastrophic failure, which could result in injury or death.

Both the walls and footing lack reinforcement in the correct arrangement to resist the soil loading.

I would expect the wall to develop horizontal cracks over time as the soil pressure exceeds the capacity of the wall, or for the wall to start sliding, as it lacks proper connection to the footing.

3/. No wall waterproofing membrane

The masonry will absorb moisture and start to fret.  This will contribute to a reduced lifespan of the structure.

Final thoughts

I LOVE the idea of a bunker.  I wish I could build one on the cheap in my backyard (not taking into consideration legal requirements for building rules, proper structural design, and the missus approving the budget.  But it has to be done RIGHT or you are just building yourself a giant liability at best or a death trap at worst.

Get a proper structural design to start with and then talk with a licensed builder to see what parts of the work you can do yourself without ending up with a terrible product.  It will not be as cheap as advertised, but it won't end up costing you a packet to demolish and rebuild once it goes down the crapper, and it won't pose a safety hazard to you and your loved ones.