If a sincere muslim commits major shirk/major kufr is he labelled a mushrik/kafir

In footnotes of the translation of book "Bad al amali" it's mentioned that if a believer commits grevious sin he isn't a disbeliever. > We, the Ahl al-Sunnah say that regardless of the enormity of a person’s sin, he remains a believer; and Allāh may punish him or forgive him. Additionally the ***SINCERE*** muslims among bani israil who worshipped calf weren't labelled mushrikun in quran. Another relevant incident from sunni corpus is about a man who asked his sons to burn him and disperse his ashes in the sea so that Allah cannot catch him . Isn't this major kufr to deny the ressurection ability of Allah? I am not sure the incident of prophet Adam eating from the tree can fit the above category. Therefore the question are sincere muslims not labelled kaafir/mushrik if they commit major shirk/major kufr. I am not taking into consideration the concept of ***Establishment of proof*** since I am asking this question for sincere muslims only. Sincere muslims promptly accept the mistake once told .