The report sites a lot of papers, many of which by one report author Hoegh-Guldberg who has been studying reefs and claiming they are at risk since at least 1999. One of the latest of those papers puts it like this (ideas which the article does not accurately represent):

  "Even if the goals of the Paris Climate Agreement are achieved, coral reefs are likely to decline by 70–90% relative to their current abundance by midcentury."

  "Although alarming, coral communities that survive will play a key role in the regeneration of reefs by mid-to-late century. Here, we argue for a coordinated, global coral reef conservation strategy that is centred on 50 large (500 km2) regions that are the least vulnerable to climate change and which are positioned to facilitate future coral reef regeneration."

Hoegh-Guldberg, Ove, Kennedy, E. V., Beyer, H.L., McClennen, C., Possingham, H.P., 2018. Securing a Long-term Future for Coral Reefs. Trends Ecol. Evol. 33, 936–944. https://doi.org/10.1016/j.tree.2018.09.006

They are not "doomed" they are "at risk".