Should be easy to find one example if your claim that “mutation eventually leads to extinction” has ANY bearing upon reality.
Humans have evolved, and it is not “degenerative” or devolution. If it is, then the most advanced humans with the least “degenerative” genes are those with a fully functioning set of genes for skin melanin. Thus Black people are the least mutated and most perfect as God intended humans to be, and any change from that is because this is a “fallen” world where light skin results from the devolution of a full set of functioning skin melanin genes.
I have yet to hear a Creationist embrace this logical conclusion of their degenerative hypothesis of genetic change. Will you be the first?
And when has mutation eventually led to extinction? Did the dinosaurs mutate themselves out of existence according to your “scientific” creationist “theory”?
Whatr about bald eagles? They would be extinct if it weren't for human intervention. A genetic fault made their egg shells weak. There are living examples of endanged animals that have developed a genetic defect, and because of their small gene pool, there is no longer a source of a stronger one. So they are sickly and need to be bred in captivity.