I think it is the same issue we saw here `register` fails if `-fplugin=Foo` is used in `ghc-options:` · Issue #9375 · haskell/cabal · GitHub
There was an old workaround for an issue with ghc-cabal (which is now gone). The workaround was to not pass -package-db to GHC when calling --abi-hash. It used to be unnecessary but with GHC 9.6 the plugin initialisation happens earlier than before, and this means we do need to pass -package-db.
We removed the workaround in Revert #3639 (Don't pass -package-db and -package flags to --abi-hash) by andreabedini · Pull Request #9384 · haskell/cabal · GitHub only two weeks ago. We could do a minor release but our “release pipeline” is a fair bit of manual work … :-/