Here is the theme:
The logo is an abstract representation of the flag colours of the 41 countries participating in 2020 in order of their first participation. The logo builds on the design of previous editions of the Eurovision Song Contest that were held in the Netherlands.
Love how it's a modern twist on the classic logo used by the Dutch at the 1970, 1976 and 1980 contests
Plus the logo representing all 41 countries with their flag colours is a nice touch