If I understand correctly, all bishop ordinations must be approved by the Holy See. How are schismatic bishops’ ordinations valid if they don’t get permission from the Holy See? I am speaking of Orthodox and SSPX, for example.
If a bishop is validly ordained, he has the power to ordain another bishop by the fact of his episcopal ordination. But in order for that episcopal ordination to be licit (i.e., lawful), a Catholic bishop must have permission from the Pope to ordain a bishop. If he does not have permission, the ordination is presumed valid (i.e., a true ordination) but is illicit.