See subject. “Established” means good-old flourishing genetically healthy, more or less, health-enough-to-reproduce-indefinitely species.
I’m sure my assumptions even in choice of words in query are screwy.
Inbreeding is maladaptive. Except when it isn’t.
New species are established by inbreeding. Except when they aren’t.
The transition from the parent species to the new species may be gradual, allowing for plenty of genetic diversity even as the speciation proceeds.
Speciation usually occurs within a population rather than within a single individual, making inbreeding an nonissue. There are times where it is an issue, like when a species or population undergo a bottleneck or founder effect. The answer there is simply that even though inbreeding is bad for the health of the population, it’s not bad enough to wipe them out completely. Some survive and the species continues.
I’d agree with this part. Inbreeding isn’t always madadaptive - the impact of it is that it can lead a rare, recessive gene to express.
Usually this isn’t advantageous to the offspring, and many rare, recessive genes can be harmful. However, like mutations, sometimes one is beneficial.