Try using a named volume on Prosody to see if it helps with permissions.

Config/Prosody/docker-compose.example.yml

@@ -1,6 +1,14 @@
 # 2026-06-11 Hyperling
 # Configuration for running a Prosody XMPP server.
 
+volumes:
+  prosody_data:
+    driver: local
+    driver_opts:
+      type: none
+      device: ../../Volumes/Prosody/data
+      o: bind
+
 services:
   app:
     container_name: prosody
@@ -23,7 +31,7 @@ services:
     #  retries: 2
     #  start_period: 30s
     volumes:
-      - ../../Volumes/Prosody/data:/var/lib/prosody/
+      - prosody_data:/var/lib/prosody/
       - ../../Volumes/ReverseProxy/letsencrypt/live:/etc/letsencrypt/live
     deploy:
       mode: global