Yes, I was searching the Scriptures and the web last night about despair equals sin. Someone mentioned it on Christian radio last night, and I’ve never heard of such a thing before in my Christian life.
I found many Catholic references to “sins against hope” including despair and presumption, but none of those references claim Scripture as the source.
Of course, Jesus often says be of good cheer and be not afraid. So I’m guessing if you violate these commands, they are sins. But Jesus never described these commands that way.
Job 24:22 Yet God prolongs the life of the mighty by his power; they rise up when they despair of life.
2 Corinthians 1:8-10 For we do not want you to be unaware, brothers, of the affliction we experienced in Asia. For we were so utterly burdened beyond our strength that we despaired of life itself. Indeed, we felt that we had received the sentence of death. But that was to make us rely not on ourselves but on God who raises the dead. He delivered us from such a deadly peril, and he will deliver us. On him we have set our hope that he will deliver us again.
I don't see condemnation for despair anywhere in Scripture.