Reef Fishes of the East Indies (Allen & Erdmann) has been mentioned before as a 3 volume book set. But you can also get it in digital form as an app for iOS and Android, and for macs with Apple silicon CPU. I use it on a Macbook where it occasionally crashes but is still my favorite travel resource. You can download one of the 3 volumes for free and if you like it, which I expect you will, you can buy the other two for US$18 each.
https://www.reeffishesoftheeastindies.com/
If you were thinking to get the actual books then perhaps hold off because the second edition is at the printer. Hundreds more species have been added, some of them described in the appendix of volume 3, names updated and geographic distributions adjusted based on new data. Unfortunately I don't think an electronic version will accompany the books, at least not immediately.