Not provided in Zitadel. Keycloak either. WSO2 IS has it. I hate WSO2 with a passion but it does SCIM.
A non-Java on-premises IS is certainly welcome. Haul in SCIM and I'll take a swing at it.
If anyone else wants to look at software supporting SCIM, this list seems like a place to start: http://www.simplecloud.info/#Implementations2 It lists both SCIM servers (which can be the source of truth for a set of users and groups) and SCIM clients (which can received CRUD requests from a SCIM server).
(I submitted our company to the list but I think they got caught up in the GitHub/Heroku situation, since changes in the GH repo don't seem to be going live: https://github.com/erdtman/simplecloud.info )
An wonderful piece of work. Note, however, that the most recent supported Keycloak version is 16.1.x. Whereas Keycloak has recently been reworked (beginning with 17.x, now at 18.x) around Quarkus. This is awkward to explain to stakeholders that understand the implications of having their authentication system held back due to dependencies.
SCIM is a well designed and standards based (RFCs even!) expression of identity management in REST. Expecting identity platforms to support it as a first class capability is reasonable.
We definitely have SCIM2.0 on the radar. If someone feels intrigued we would happily accept a PR