Same issue here. I have activated PO on the specific schema where the materialized view resides per these instructions https://docs.databricks.com/aws/en/optimizations/predictive-optimization#check-whether-predictive-op...
- Doesn't help with the issue

Problem hypothesis: DLT (newly renamed to lakeflow declarative pipelines) is not creating Unity Catalog Managed Tables, which is a pre-condition for Predictive Optimization, which in turn is a pre-condition for automated liquid clustering. 

Context:
- Predictive optimization is enabled on the account and the specific unity catalog schemas used
- Other tables (non-DLT created) in the schemas are Unity catalog managed (see image) and then unity catalog shows the validation in the UI.See image below:

Proof of PO being activated for the schema

Question
- Is DLT not capable of creating unity catalog managed tables?