How to write a proper project finalizing email?

Yes, I would absolutely write a celebratory email 🎊 What to include:

• Why should people care? Talk about the benefit of the project, either for other developers or users. Talk about the metrics you looked at and why it'll help the company.
• Call out anyone and everyone who contributed. This has two benefits: (1) make your collaborators feel good and (2) remind people about the project (e.g. they may have helped you with some feedback/code review months ago but forgot the project).
• Next steps. Talk about the next steps in the project, and why it's exciting. Your goal is to present a narrative about something bigger.

We talk about some of these concepts here: [Masterclass] How To Build Deep Relationships Quickly In Tech

You should definitely write the email! In 99.9% of cases, bringing visibility and claiming credit is all upside, no downside.

In terms of the structure of the email, I recommend checking out my answer here on how to write a good Workplace post (Workplace is specific to Meta, but the structure is generic): "How to get more visibility on work?"

If English isn't your first language (or you just have some reservations about your English in general), you can use ChatGPT to catch basic spelling/grammar/syntax errors.

Given that this is a launch announcement, I highly recommend attaching an awesome demo as well - Video if you can. Everyone loves demos, especially executives.