Hey @JCW - if I were to guess, based on your other question (here) these dates are multi-value fields (something possible in SmartSuite) and it’s probably preventing us from Sorting on them, at least not without more work.
We definitely do support sorting and filtering by date fields in SmartSuite, but it may be nuance with your date field.
If you could reach out to our support team with details of the page and the fields in question we can confirm this and look into it for you.