The Catholic church forbids the use of condoms because their purpose is to prevent conception - maybe a hangover from times long ago when the population was small and under threat; procreation was encouraged for everyone as it was necessary to continue the human race.
Condom use between people of the same sex would make no difference to the chances of conception, though sex between people of the same sex might distract them from activities that would result in procreation, and so might be looked on with disapproval by those concerned about the continuation of humanity.