internet slang. 美腻=美丽, due to the similarity in pronunciation. 美丽死了 means stunningly beautiful. It sounds cute, adorable, or sometimes humorous to use 美腻 instead of 美丽, under informal circumstances. I think it is most suitable for girls to use. Not a very manly word. Hope this helps.

Very beautiful！！

English has a "fricking" to put ahead of adjective for a emphasis purpose. “形容词+死了” has the same effect. But I barely heard of "美腻死了", "美/漂亮死了" is more commonly said

漂亮极了 so beautiful

“美丽死了” It means : the most beautiful or the most pretty. “死” is not really dead,