Are the concepts of a chemical element and a simple substance identical? Explain with an example.

No, the concepts “chemical element” and “simple substance” are not identical. I will explain in simple words. Chemical element – an element from the periodic table. For example, H. Simple substance is a substance consisting of atoms of a chemical element. For example H2.
Thus, H is a chemical element, H2 is a simple substance.

A chemical element is the most capacious concept that includes all possible forms of existence of chemical particles with the same nuclear charge: individual atoms in the form of all their isotopes, ions in the form of cations and anions, other particles participating in the formation of simple and complex substances, due to the modification of their electronic shells.

Matter is what physical bodies are made of. It is one of the forms of matter.
Allocate simple substances consisting of atoms of one element
For example, О2, Сl2, N2
And complex substances consisting of atoms of two or more elements
For example, H2O, CO2, C6H12O6
An element is a collection of atoms with the same charge of atomic nuclei
Elements are presented in the periodic table
If you say: “Oxygen is a gas”, then it is clear that this substance
If we say: “Oxygen is part of water”, then here we can conclude that oxygen is an element