Hey Karol,
This is a fairly common question so smarter people than I have answered it online. The internet, windows/mac are gamma 2.2 instead of gamma 2.4. This is causing the difference in your viewing. There a variety of ways to interpret and deal with this change within resolve before exporting. A quick google and I found this article which seems to cover the basics well:
https://mixinglight.com/color-grading-tutorials/gamma-2-2-vs-gamma-2-4-davinci-resolve/
It has also been covered on here and other forums many times.
Hope that helps,
Kurt
