Finished artwork or an editable template?
Not every design needs to be editable. If the content is unlikely to change, finished artwork in the agreed format may be the simplest answer.
Repeated communications are different. Your team may need to change an event date, replace a photograph, create the next post in a series or prepare a new presentation without rebuilding the design each time. In those cases, an editable template can be more useful.
I mainly use Adobe applications, but I am happy to discuss the tools your organisation already uses. Depending on the job, that could mean a template in Canva, Affinity, PowerPoint or another suitable application. I generally recommend other tools for design templates, though Word can be the right choice for a working letterhead.
The useful question is, “Who will edit this, what will they need to change and what can they use confidently?” The right format and handover depend on those answers, because not every design transfers neatly between applications.