Is despairing of Allah's mercy considered disbelief (kufr), based on His saying in Surat Yusuf: "Indeed, none despairs of the relief of Allah except the disbelieving people"?

Despairing of Allah's mercy may constitute disbelief if hope is entirely absent, and if it entails denying the Quran and entertaining ill thoughts about Allah, for He says: ﴿And My mercy encompasses all things.﴾ It may also be a major sin if it stems from deeming one’s sins or Allah's decree as insurmountable, while hope still remains, for Allah Almighty says: ﴿Indeed, no one despairs of relief from Allah except the disbelieving people,﴾ and His saying, glorified be He: ﴿And who despairs of the mercy of his Lord except those astray?﴾