I said the work was protected by US copyright law, not that US copyright law would necessarily be used in the case. That the opera is a US work can be relevant to jurisdiction rather than the case in chief.

Copyright would probably not be an issue. This looks like a simple contract dispute, a debate re whether one party is abiding a term in a licensing agreement.

Are people obliged to abide by an obviously racially discriminatory contract under EU law?

If EU law is applied, no. If American law control, probably yes. This is a contract between an american and an EU organization so there will be a fight over which law controls the contract. Due to the split between the various US states, American contracts normally have some language stating which jurisdiction's laws should be used to interpret the contract. If this was a stock licensing deal from the estate it probably names a US state.