The suet and offal of the animals of which its meat is lawful is permitted to eat. There’s no evidence on the prohibition of these. In the 146th verse of chapter An’am, the prohibition of cattle’s suet to Jews is stated:
”And to those who had Judaized, We have forbidden all beasts with claws, and the suet of cattle and sheep except which is either on their backs or their intestines, or that mixed up with bones. It is Our punishment to them for their rebellion. Surely We state the truth.” (Al-An’am/The Cattle 6:146)
What is prohibited for Muslims is mentioned in the previous verse and suet isn’t included in it.
“Say: I cannot find in what has been revealed to me anything forbidden for anyone who wants to eat unless it is carrion, outpoured blood and the flesh of swine, all of which is unclean; or that which is profane having been slaughtered in a name other than that of Allah. But whosoever is constrained to it by necessity -neither desiring to disobey nor exceeding the limits- (let him know that) your Lord surely is the Forgiver and the Merciful.” (Al-An’am/The Cattle 6:145)