I was able to solve this issue by changing my code from

@Configuration
@EnableTransactionManagement
public class Neo4jConfig {

    @Bean
    public Neo4jTransactionManager transactionManager(org.neo4j.driver.Driver driver) {
        Neo4jTransactionManager manager = new Neo4jTransactionManager(driver);
        manager.setValidateExistingTransaction(true);
        manager.
        return manager;
    }
}

to

@Configuration
@EnableTransactionManagement
public class Neo4jConfig {

    @Value("${spring.data.neo4j.database}")
    private String database;

    @Bean
    public DatabaseSelectionProvider databaseSelectionProvider() {
        return () -> DatabaseSelection.byName(database);
    }

    @Bean
    public Neo4jClient neo4jClient(Driver driver, DatabaseSelectionProvider provider) {
        return Neo4jClient.with(driver)
                .withDatabaseSelectionProvider(provider)
                .build();
    }

    @Bean
    public PlatformTransactionManager transactionManager(Driver driver, DatabaseSelectionProvider provider) {
        return Neo4jTransactionManager.with(driver)
                .withDatabaseSelectionProvider(provider)
                .build();
    }
}

I found this on a Chinese website, along with an explanation: https://leileiluoluo-com.translate.goog/posts/spring-data-neo4j-database-config-error.html?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=sv&_x_tr_pto=wapp