Will Allah accept the repentance of a disobedient person who committed major sins and immoralities for a long time, then repented with sincere repentance, and will his repentance save him from the torment of the grave and hellfire?

A Muslim should not consider their sin that they have repented from to be great, because Allah's mercy is greater, and sincere repentance expiates sins. If the sin involves the rights of other people, those rights must be restored. If the sin is between the servant and their Lord, then repentance, remorse, and the firm resolve not to return to it are sufficient. It is not a condition for the completion of repentance that the prescribed punishment (حد) be carried out on the repentant person; rather, concealment (ستر) is better. Sincere repentance transforms evil deeds into good deeds, as mentioned in Surat al-Furqan. If the prescribed punishments (حدود) have not reached the authorities, then concealment and repentance are preferable. However, if they have reached the authorities and been proven, then their implementation becomes obligatory and is not waived by repentance.