When the body goes without carbohydrates for a long time, it switches to burning fat for fuel.

Fun fact, we store fat for energy. When we sleep, between meals we are always burning fat. Babies burn fat for fuel all the tiem.

to save what little glucose it has for the brain, the muscles temporarily become “insulin resistant.”

Insulin resistant is the wrong term here, the body is not flooded with high levels of insulin in a fat metabolism. The proper term is glucose sparing, most of the body is going to burn fat for energy in this state with the major exception being red blood cells and about 5-15% of brain energy.

fail a standard oral glucose tolerance test.

Will fail a improperly administered oral glucose tolerance test, OGTTs must be primed for accuracy. The body's response to insulin is very sensitive, but the pancreas isn't maintaining a hot cache of insulin, because you arn't using very much insulin. We have discussed this in detail before https://lemmy.world/post/46537093 . This is normal, your body doesn't waste energy. This has no negative downsides because the pancreas will just make more glucose on demand when you consume carbohydrates and elevate glucose levels, and fill up the quick release cache.

High intake of certain saturated fats can sometimes lead to an accumulation of fats inside muscle and liver cells (called intramyocellular lipids).

Citation please - typically this condition is caused by super high elevated insulin levels and full fat cells (and the fat has nowhere to go) typically in a pre-diabetic state.

This buildup can interfere with insulin signaling, potentially worsening cellular insulin resistance under the hood.

The fat in the muscles wont cause insulin signaling issues, your confusing cause and effect. The fat is ectopically stored around the body BECAUSE of the elevated insulin. visceral fat, intramuscular fat is a hallmark of metabolic dysfunction caused by hyperinsulinemia. In fact this is EXACTLY how marbled meat is made in cows, they are forced to eat excessive carbohydrates leading to this very condition

While a carnivore diet frequently causes a drop in blood sugar levels because you aren’t eating sugar, it does not automatically make someone immune to developing insulin resistance or diabetes over the long term.

Citation please - How can a diet without elevated blood glucose, and thus without elevated insulin lead to a condition of carbohydrate intolerance (type 2 diabetes). I already addressed the failings of a unprimed OGTT above in the ketogenic post i linked .