﴿ مِّمَّا خَطِيٓـَٰٔتِهِمْ أُغْرِقُوا۟ فَأُدْخِلُوا۟ نَارًۭا فَلَمْ يَجِدُوا۟ لَهُم مِّن دُونِ ٱللَّهِ أَنصَارًۭا ﴾

“And so, because of their sins, they were drowned [in the great flood], and were doomed to suffer the fire [of the hereafter]; and they found none who could succour them against God.”

Because of mimmā mā indicates a relative clause their iniquities khatāyāhum a variant reading has khatī’ātihim they were drowned by the Flood then made to enter the Fire with which they were punished underwater after drowning. And they did not find for themselves besides that is to say other than God any helpers to protect them against the chastisement.