raise hand I HAVE A QUESTION!!
on page 6 the tree bark is that true Can it be used in real life? or is bullshit cooked up by Author ass?
The picture where the bark container is put straight on the flames is bullshit, that's not how you do it. Tree bark is flammable, and although the water will transfer a lot of heat, the outside will soon catch fire unless the tree is a fireproof isekai tree. And don't strip a living tree as huge as the MC does, in most cases the bark will be thick and cracked up as you can see in the bottom picture. He could probably use it on the roof of a shelter, but I doubt that he could make a cooking vessel. Maybe if he manages to split it and only use the innermost bark layer, but that will be difficult with just Homo Habilis tools.
I don't know what kind of tree he stripped, but birch bark is the best to make containers from (I have several, birch is the most common tree here) and it definitely wasn't that. If you have to boil water in one, make a fire and put some clean rocks in the fire. When they're good and hot, put one into the water until it stops sizzling, take it out and put another in etc. until the water boils.
I took a quick look on the first of baconcat's videos, and they used a birch bark vessel which they put in the embers, not directly on the flame. Still dubious, birch bark is one of the best tinders you can find, but they only quickly warmed a tiny amount of water, enough for one cup of tea. So it went well, but that vessel were single use only.