Are the slaughtered animals from countries where people of innovation (Ahl al-Bidʻah) are prevalent, and which have the word "halal" printed on their packaging, considered halal or not? And are there differences among scholars' opinions regarding their authenticity?

The basic rule is that the slaughtered animals in Muslim lands are permissible, because the fundamental principle for those who profess Islam is the validity of their Islam, even if they are innovators (ahl al-bid'ah), as long as their innovations are not considered apostasy-inducing. Moreover, someone who is attributed to deviant sects may not actually adhere to their principles, or may be ignorant, so a ruling of disbelief or فسق (transgression/immorality) cannot be issued against them until after evidence has been established against them and any ambiguities removed. If evidence is not established against them, they remain upon the original state of Islam, and thus their slaughtered animals are permissible. The ruling is based on the predominant situation, even if the existence of apostasy-inducing innovations is known.