Respected Sister, Salam!
Here is a better understanding. Please also note that none of the noble companions of the exalted prophet ever uttered a single word of denial or doubt even under severest persecution.
16:105 It is those who reject God’s Messages that invent this falsehood. And it is those who are lying.
16:106 (Exempted is) one who, after attaining belief in God, utters ingratitude to Him under compulsion with his heart remaining fully contented in belief. But if someone opens his heart to denial, for such there is God’s requital, and theirs is an awful doom. [‘Kufr’ = Denial, ingratitude. 6:145]
QXP GLOSSARY: Kufr = Opposing the truth = Denying the truth = Concealing the truth = Ingratitude = Rejection of truth = Choosing to live in darkness = Hiding or covering something = Closing eyes to light. Kaafir = One given to Kufr = One who adamantly denies the truth = One who opposes the truth = Commonly translated as ‘infidel’ = Derivatively, a farmer who hides the seed under the soil (57:20). Therefore, Kufr or Kafir does not apply to the unaware, anyone to whom the Message has not been conveyed or reached yet.