Confusion surrouding Einsteins explanation of The theory of special relativity [closed]

For context, i currently study chem in uni and the theory of special relativity came up shortly which had me trying to figure out what it was out of natural curiosity. The videos and explanations ive seen still didnt help me so i bought a book a book with a copy of the theory in it and have been reading through it.

The issue is here is that while im not far into it, Einstein seems to keep making the same "mistake" in the book. He assumes an observes perspective is somehow their own "truth". For instance he mentions a person on a train traveling at a constant velocity v, and light traveling at the speed of light c next to it.

He rightfully comes to the conclusion that the observer will experience the light being slower, but he goes on to assume this somehow means that the light was actually slower by saying this contradicts the principle of relativity that states that the laws of physics will remain constant regardless of space and place, which is what i believe so far to be a misconception.

This is because while the observer did infact have a unique perspective on the laws of physics which would suggest to that observer that the laws of physics were not consistent, the laws of physics didnt actually change. The observer and/or the train moving at a v did not have an effect on c, that is, they did not change or interact with light in a way that changed c or the laws of physics. c remained the same velocity, and therefore, the observer on the train was not under the influence of different laws of physics.

It should, as i believe so far, be concluded that observers should be seen as completely irrelevant when trying to find a truth. It is completely common in all aspects of reality and life that observers may experience different perspectives to something that has a definitive state. For instance, if two observers were placed at either side of a irregularly shaped building, they may perceive and report the building as having a different shape, despite that building having a definitive true shape.

As i continue to read the theory of special and general relativity, i hope to uncover and solve my confusion, but until and only if that comes, please would someone point out how i am wrong here. Thank you.