The Theory of Evolution is not absolutely true. The theory of atoms is not absolutely true. The theory of heat exchange is not absolutely true. Absolutely true is not a term that should ever be used in a science education. If we can't teach anything in a science classroom that is not "absolutely true", we can't teach anything.
What the three theories I mentioned have in common:
- They are strongly supported by predicted observations.
- There are no alternative theories that are as strongly supported by predicted observations.
These two traits combine to make what is called a "scientific fact". That is not a fact in the logical sense of the word, but is in fact defined by just these two traits. When someone says "scientific fact", that's what they mean. Sometimes deep in a scientific conversation the word "scientific" might get dropped and they will just be referred to as "facts". Perhaps that is where some confusion comes from.
This is not true in the case of Evolution. In fact, the theory of Evolution makes several predictions which are not observed. For example, current speciation in the biosphere. We should be seeing it, the theory predicts it, and there is absolutely ZERO evidence of it.