What charges can never be sealed in Florida?

Two separate barriers.

A conviction. If adjudication was entered rather than withheld, sealing is generally unavailable. That's why DUI convictions can't be sealed — Florida prohibits withholding adjudication on a DUI, so the mechanism that would allow sealing never exists.

The excluded offense list. Florida law enumerates offenses that cannot be sealed even where adjudication was withheld. The list includes serious violent offenses, sexual offenses, offenses against children, and others.

The practical consequence is significant at the plea stage. Whether a particular disposition preserves sealing eligibility should be part of the negotiation, and it's frequently more consequential than the length of probation attached.

Note the interaction with automatic sealing: that provision has its own eligibility criteria, keyed to forcible felonies and registration offenses, which are not identical to the court-ordered exclusion list.