Static service not working when using SCAN?
Static registration is no longer required starting with 12.1.0.2, as the DG broker uses Grid Infrastructure to restart instances. Of course, if you have a single instance database without Grid Infrastructure, there it is still required.
Oracle Data Guard Broker and Static Service Registration (Doc ID 1387859.1)
Also in the above document:

From 11.2 on, never register the entries with the SCAN listener as it
is not associated with a specific host.

I have never seen anyone using static registration in SCAN listeners, so I had to try this myself. On a 2-node cluster with 3 SCAN listeners, I added the below to listener.ora, first node:
SID_LIST_LISTENER_SCAN1,SID_LIST_LISTENER_SCAN2,SID_LIST_LISTENER_SCAN3=
 (SID_LIST =
  (SID_DESC =
   (GLOBAL_DBNAME = TEST_SERVICE)
   (ORACLE_HOME = /u01/app/oracle/product/19.0.0/dbhome_1)
   (SID_NAME = TEST1)
  )
 )

Second node:
SID_LIST_LISTENER_SCAN1,SID_LIST_LISTENER_SCAN2,SID_LIST_LISTENER_SCAN3=
 (SID_LIST =
  (SID_DESC =
   (GLOBAL_DBNAME = TEST_SERVICE)
   (ORACLE_HOME = /u01/app/oracle/product/19.0.0/dbhome_1)
   (SID_NAME = TEST2)
  )
 )

Yes, it worked, but I would still not do it because of the above reasons.