Add endpoint that uses plone.volto indexer

src/plone/restapi/services/blocktypes/configure.zcml

@@ -0,0 +1,15 @@
+<configure
+    xmlns="http://namespaces.zope.org/zope"
+    xmlns:plone="http://namespaces.plone.org/plone"
+    xmlns:zcml="http://namespaces.zope.org/zcml"
+    >
+
+  <plone:service
+      method="GET"
+      factory=".get.BlockTypesGet"
+      for="zope.interface.Interface"
+      permission="zope2.View"
+      name="@blocktypes"
+      />
+
+</configure>

src/plone/restapi/services/blocktypes/get.py

@@ -0,0 +1,39 @@
+from plone import api
+from plone.restapi.services import Service
+from collections import Counter
+from plone.dexterity.content import get_assignable
+
+
+class BlockTypesGet(Service):
+    def reply(self):
+        catalog = api.portal.get_tool(name="portal_catalog")
+        request_body = self.request.form
+        result = {}
+
+        if request_body.get("blocktypes") != "":
+            blocktypes = request_body.get("blocktypes").split(",")
+
+            for blocktype in blocktypes:
+                brains = catalog.searchResults(block_types=blocktype)
+                result[blocktype] = Counter()
+
+                for brain in brains:
+                    obj = brain.getObject()
+                    assignable = get_assignable(obj)
+
+                    hasBlocksBehavior = bool(
+                        {
+                            behavior
+                            for behavior in assignable.enumerateBehaviors()
+                            if behavior.name == "volto.blocks"
+                        }
+                    )
+
+                    if hasBlocksBehavior:
+                        url = brain.getURL()  # or brain.getPath()
+
+                        for block in obj.blocks.values():
+                            if block["@type"] == blocktype:
+                                result[blocktype].update({url: 1})
+
+        return result

src/plone/restapi/services/configure.zcml

@@ -13,6 +13,7 @@
   <include package=".actions" />
   <include package=".addons" />
   <include package=".aliases" />
+  <include package=".blocktypes" />
   <include package=".breadcrumbs" />
   <include package=".content" />
   <include package=".controlpanels" />