Use version marker to define if is Plone 6

src/plone/restapi/__init__.py

@@ -1,8 +1,8 @@
 from . import patches  # noqa: ignore=F401
 from AccessControl import allow_module
 from AccessControl.Permissions import add_user_folders
+from importlib import import_module
 from plone.restapi.pas import plugin
-from Products.CMFPlone.utils import getFSVersionTuple
 from Products.PluggableAuthService.PluggableAuthService import registerMultiPlugin
 from zope.i18nmessageid import MessageFactory
 
@@ -22,7 +22,9 @@
 allow_module("json")
 
 # BBB: Plone 5.2
-PLONE5 = getFSVersionTuple()[0] == 5
+HAS_PLONE_6 = getattr(
+    import_module("Products.CMFPlone.factory"), "PLONE60MARKER", False
+)
 
 
 def initialize(context):

src/plone/restapi/imaging.py

@@ -1,15 +1,15 @@
-from plone.restapi import PLONE5
+from plone.restapi import HAS_PLONE_6
 from zope.component import getMultiAdapter
 from zope.component import getUtility
 from zope.globalrequest import getRequest
 
 
-if PLONE5:
-    # BBB: In Plone 5.2, it is necessary to use the direction parameter.
-    scale_parameter = {"direction": "thumbnail"}
-else:
+if HAS_PLONE_6:
     # In Plone 6.0+, we must use the mode parameter
     scale_parameter = {"mode": "scale"}
+else:
+    # BBB: In Plone 5.2, it is necessary to use the direction parameter.
+    scale_parameter = {"direction": "thumbnail"}
 
 
 def get_scales(context, field, width, height):