Tsugumi-sama
This is Kawaguchi Hidetoshi. This is a humble answer to the question.
Not everything is an “illusion,” and everything, including “suffering,” is sometimes expressed in Buddhism as “something like an illusion.”
The point is that it is “like,” or “like,” and it is not equal to illusion. Of course, there are also real illusions. Mirages, runaway waters, events in dreams, etc.
Also, even though it is an illusion, it actually has effective effects and functions; for example, if you touch ice, it's cold, and if you get caught by fire, you'll get burned hot. Ice and fire are illusions, and there's no way you can put up with it; cold things are cold, and hot things are hot.
Naturally, there is no change in the fact that suffering is suffering as long as you have actually experienced the effects of suffering.
However, speaking of where did such suffering come from, it does not suddenly appear from a place where there is no cause or condition, and there is always a causal relationship (cause and condition) leading to that suffering, then if the causal relationship that brings about that suffering is adjusted to a causal relationship that destroys suffering, suffering will naturally also be destroyed.
If it's cold and causes suffering, it means a cause relationship that warms you; if it's hot and painful, it means a cause relationship that cools you down.
After all, suffering can be destroyed by cause and effect. Buddhism is the teaching for reconciling that cause and effect.
I would be grateful if you could continue with your Buddhist practice.
Kawaguchi Hidetoshi Gassho