There are various bodies involved in the certification of the different elements involved in eSIM applications.
The GSMA operate a scheme called Security Accreditation Scheme ( SAS ) that provides a certification of the site belonging to an organisation that provides Remote SIM Provisioning services. Details of the scheme and a list of approved sites is available on their web site.
GlobalPlatform tests and lists the actual certified eUICC chips on their website. Select “eUICC” from the dropdown to see the eUICCs that are currently approved.