Here is an article I just read: https://www.ilpost.it/2023/05/31/djokovic-kosovo-serbia/
Given all the definitions of the words esprimere, esprimersi, and espresso in pons.com and collinsdictionary.com, I don't see how "il controverso presidente della Bosnia-Erzegovina" can be "espresso dall’etnia serba". Obviously, the guy comes from that ethnicity, from that community, but is espresso the best way to express that? Maybe they should have said "proveniente da" or "che viene da" instead.
The phrase is correct and usual.
"il controverso presidente della Bosnia-Erzegovina espresso dall’etnia serba", actually, doesn't mean that "he comes from this ethnicity".
Instead, it means that this president has been, in a sense, 'produced', probably through elections, by this ethnicity and represents it, regardless his ethnical origin.
It means 'è manifestazione di.., proviene da.., è prodotto da (but not necessarily through elections).
It is one of the meanings of the verb esprimere: to produce, to generate:
Treccani (lett.) spremere, trarre fuori, generare, far nascere
Hoepli 3. (lett.) spremere fuori, estrarre: esprimendo dai fiori la stilla essenziale (d'annunzio) || Generare, produrre
Garzanti 3. (lett.) produrre, emanare, creare.
See https://dict.numerosamente.it/definizione/esprimere
A synonymous could be essere espressione di or essere emanazione di: provenire da, essere prodotto da, derivare da: for example un provvedimento emanazione di un gruppo.
A sua volta da emanare:
https://www.google.com/search?client=firefox-b-d&q=emanare+treccani
The dictionaries quoted above say that, in this sense, it is a literary term, but in some expressions, as in your case, this is not literary, but is usual. For instance, it is usual when used in a political context, for example un governo espresso dalla minoranza. See:
https://dizionario.internazionale.it/parola/governo-minoritario
