Are the following actions considered an act of disbelief (kufr): avoiding riding in a car that has a cross emblem for fear of disbelief, collecting discarded papers that have religious symbols without explicitly denouncing those who discarded them, and not checking a discarded paper that might contain religious symbols?

Merely riding in a vehicle bearing a cross does not constitute acceptance of disbelief (kufr) nor does it necessitate apostasy (riddah). The same applies to leaving a piece of paper whose content is unknown. Apostasy is the opening of one's heart to disbelief, as Allah Almighty says: "Whoever disbelieves in Allah after his belief — except for one who is forced [to renounce his religion] while his heart is secure in faith. But those who open their hearts to disbelief — upon them is wrath from Allah, and for them is a great punishment." (An-Nahl: 106). One who has entered faith with certainty does not exit it except with certainty. And whoever performs an action that could be interpreted as apostasy or otherwise, is not deemed an apostate for it, in accordance with the principle of averting prescribed punishments (hudud) and doubts from Muslims.