basic structure with test advancement

Custom_Advancements_1.21/data/custom_advancements/advancement/test/test.json

@@ -0,0 +1,28 @@
+{
+    "display": {
+        "icon": {
+            "id": "minecraft:stripped_dark_oak_log"
+        },
+        "title": {
+            "text": "Test",
+            "color": "blue",
+            "bold": true
+        },
+        "description": {
+            "text": "Test the datapack!",
+            "color": "blue",
+            "italic": true
+        },
+        "frame": "challenge",
+        "announce_to_chat": true,
+        "background": "minecraft:textures/block/netherite_block.png"
+    },
+    "criteria": {
+        "joined": {
+            "trigger": "minecraft:tick"
+        }
+    },
+    "requirements": [
+        ["joined"]
+    ]
+}

Custom_Advancements_1.21/pack.mcmeta

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+{
+  "pack": {
+    "pack_format": 48,
+    "description": "Adds new advancements!"
+  }
+}