Or perhaps he is simply talking about sin, which would make sense since that is a central theme of the epistle.
And up earlier in First John chapt 2 God tells us that Jesus Christ takes care of all that for us.
And then LATER, John goes further in his explanation about the forgiveness of sin.
You illustrate PRECISELY what Peter warned about in 2 Peter 3:15-16.
I’d have to read 2 Peter.
But to limit it to First John I believe First John in the chapter five is talking about the sin of death that being when one leads another to spiritual death, not specific sins.
In relation to 2 Peter. You’re complicating things when they really aren’t.
Jesus saves.