try:
=ARRAYFORMULA(INDEX(SPLIT(REGEXREPLACE(A8:A12, "https?://www.|https?://|www.", ), "/"),,1))
UPDATE 1:
=ARRAYFORMULA(IFNA(REGEXEXTRACT(INDEX(SPLIT(
REGEXREPLACE(A8:A14, "https?://www.|https?://|www.", ), "/"),,1),
"\.(.+\..+)"), INDEX(SPLIT(
REGEXREPLACE(A8:A14, "https?://www.|https?://|www.", ), "/"),,1)))
UPDATE 2:
=INDEX(IFERROR(REGEXEXTRACT(A1:A, "^(?:https?:\/\/)?(?:ftp:\/\/)?(?:www\.)?([^\/]+)")))