"Everybody is saying: Bye."
Translation:Alle sagen: Tschüss.
So "alles" is masculine singular
Actually not, but that's because (a) the Wiktionary entry is wrong and (b) it's conflating "pronoun" (standing instead of a noun) with "determiner" (standing before a noun).
alles is neuter and is singular. I can't think of a use case for aller (masculine) or alle (feminine) as a pronoun -- only neuter alles "everything" or plural alle "everyone".
Masculine or feminine only make sense to me before a noun: aller Anfang ist schwer, alle Welt war dabei.
Try reporting the alternate and let them know which region.
I think this is a question of idiomatic usage and context. Without any further context, "Alle sagen: Tschüss" sounds most usual to me.
"Jeder sagt: Tschüss" points out that everyone says "bye" individually, one by one. To me, this is a very specific implication.
Therefore, I think the version presented by Duolingo is the one I'd normally use, too.
I tried Jeder and Jede (not sure which one should work in this case)
jeder would be appropriate (generic masculine).
jede (feminine) would only be appropriate if the entire group is composed of women or girls.
but neither were accepted
Please always quote your entire answer if you have a question about something that is not accepted.
Did you use the wrong verb, perhaps?
jeder, like "everyone", uses a singular verb: jeder sagt.