A good showcase makes it easy to understand the work and respond. Try this structure:
What I made: a short description and one useful preview.
My role: what you did and who else contributed.
Current stage: concept, work in progress or released.
Tools and process: the parts that helped and the parts that were difficult.
Feedback wanted: one or two specific questions.
Links and rights: a demo or repository, with credits where needed.
For collaboration posts, also state scope, availability and whether the opportunity is paid, unpaid or still undecided. Agree payment, rights and deliverables directly before starting.
Keep confidential client material out of public posts. You can explain a problem with a small anonymized example instead.