PGobject is not considered a simple type. It was before.

[blommish]

Converters using PGobject logs warnings

@ReadingConverter
    class PGobjectToFooConverter : Converter<PGobject, Foo?> {

        override fun convert(pGobject: PGobject): Foo? {
            return pGobject.value?.let { objectMapper.readValue<Foo>(it) }
        }
    }

Warning message:

Registering converter from class to class org.postgresql.util.PGobject as writing converter although it doesn't convert to a store-supported type; You might want to check your annotation setup at the converter implementation

It seems it was added as a Simple type and then removed in this commit. Was that intended?
879984d#diff-39643143ab2d0d7185fb6f633054e28a2804ba993e1ae9e4e7311bdcabae7190L158

[schauder]

It was only removed for R2DBC since the PG* types are part of the JDBC driver and therefore not present for R2DBC.

Please provide a Minimimal Reproducable Example, preferable as a Github repository. Make sure to include the database, either as an in memory database or if that is not possible using Testcontainers.

[blommish]

@schauder
https://github.com/blommish/spring-data-jdbc-test/blob/main/src/test/kotlin/no/blommish/BarRepositoryTest.kt#L42

2024-04-25T11:45:23.335+02:00 WARN 71844 --- [ Test worker] o.s.data.convert.CustomConversions : Registering converter from class org.postgresql.util.PGobject to class no.blommish.MyJson as reading converter although it doesn't convert from a store-supported type; You might want to check your annotation setup at the converter implementation
2024-04-25T11:45:23.335+02:00 WARN 71844 --- [ Test worker] o.s.data.convert.CustomConversions : Registering converter from class no.blommish.MyJson to class org.postgresql.util.PGobject as writing converter although it doesn't convert to a store-supported type; You might want to check your annotation setup at the converter implementation

[schauder]

The problem is that the simpleTypes from the dialect don't get registered with the CustomConfiguration.
And this happens because you overwrite the method that does that: AbstractJdbcConfiguration.jdbcCustomConversions()

Instead overwrite userConverters().
I created a PR to that effect for your demonstrator.