"Surely they must mean opera singers ... "

Remember, Leeneia, that a solo singer is one thing,
but a choir/chorus of singers is quite another.
Ask the music director of a really serious church choir
or of a community or professional chorus --
don't take my word for it.

Where I am staying, once or twice a week
a chorus director, professional caliber, pays a visit
and he and I talk about many things.
He can tell you
that choruses of singers throughout this great land
are being silenced because of the fear of coronavirus.

There are some tragic stories out there ,
the director told me one such,
about a chorus rehearsal with no masks or handwashing or anything,
as a consequence of which
four chorus members died of COVID-19
and many more were stricken.
If what Eliza/Senoufou is relating applies to these people,
some of them will find it difficult to impossible
to sing the way that they used to sing.