“They” can quite happily function as singular. I asked my friend about this and they gave me their opinion. They told me that they use “they” or “them” to discuss people when their biological sex is unimportant or unknown. I would like to ask them more but they have to leave. They tell me that they’ll be back later.
They (singular) say something. He/she/it says something. They (all) say something. You (all) say something. I say something. You (singular) say something. You’ll notice “he/she/it” seems to be the irregular outlier here. English is strange.