Does not interpreting al-istiwaʾ as settling or sitting, and merely saying "He istiwaʾ without kayf" while following Al-Albani and Bakr Abu Zayd, lead to kufr or zandaqa or tajahhum?

This issue is not one that pertains to declaring someone an infidel. Whoever emulates a trustworthy scholar among the known Sunnah scholars who follow the Salaf is in a state of well-being. The interpretation of "Istawa" as settling and sitting has already been discussed, and the viewpoint concerning it has been clarified.