I did some digging, and found on the Google forums that others were having the same problem [2] - and some claimed that the Etheopian telecom responsible for .ET was supposedly causing issues for Google IPs (presumably throttling them for authoritative DNS lookups). It seems that Google is now blocking all .ET domains from indexing, and that this change has been in effect for a couple of months.
I’m sharing here to create visibility, but also in the hopes that a Googler is lurking who might be able to help address the problem. I’ve been compelled to move my project to an entirely new domain in order to get back in Google, but I still hoper that the issue will be fixed and I can use my .ET domain.
[1] [https://search.google.com/test/mobile-friendly?url=https%3A%2F%2Fbookl.et%2F&url=https%3A%2F%2Fbookl.et%2F](https://search.google.com/test/mobile-friendly?url=https%3A%2F%2Fbookl.et%2F&url=https%3A%2F%2Fbookl.et%2F)
[2] https://support.google.com/webmasters/thread/142632230/page-et-cannot-be-submitted-to-google-ethiopian-domains-blocked-in-general?hl=en