Confidential work can still support a credible portfolio, but only within the permissions you have. Do not assume that removing a client's name makes every detail safe to publish. A combination of location, figures and screenshots may still identify the organisation.
Start with permission and scope
Review what you are allowed to disclose. Where uncertain, request approval for the specific material or choose a separate demonstration. Keep unpublished commercial information, credentials and personal data out of the portfolio.
Describe the problem at a suitable level of generality: the type of organisation, the challenge and the deliverable. Avoid details that are unnecessary for understanding your skill.
Explain your contribution
Use a short case-study structure: context, your role, approach, output and evidence. If results cannot be published, describe the accepted deliverable without inventing an outcome figure.
For a team project, say which part you owned. A portfolio should not imply you personally delivered an entire system when your contribution was limited to one component.
Use demonstrations honestly
A self-initiated sample can show how you work. Use synthetic data and label the project as a demonstration. Explain the assumptions and what would need further validation in a real engagement.
Google's helpful-content guidance reinforces the value of clear, trustworthy presentation. Readers should be able to distinguish evidence from illustration.
Publish fewer, more relevant examples rather than a large gallery without context. Connect the portfolio to the services you offer on your expert profile, and keep a private record of the permissions behind each published item.