The problem with templates
Canva makes it easy for anyone to produce something acceptable. That is its value and its risk: acceptable output from five people looks like five different brands unless the constraints are set first.
Set the constraints before the assets
Load brand colours as named entries, not hex codes people copy from a document. Upload the actual approved logo files, including the versions for dark backgrounds. Add the two typefaces you use and delete nothing else, because an unlisted font is an invitation.
Build starting points, not finished pieces
Create a small set of templates for the formats you actually publish weekly. Fewer templates used correctly beats a large library nobody navigates. Name them by use, not by design, so people choose by need.
Decide what is locked
Agree which elements can be edited and which cannot. Logo placement, colour and type are usually fixed. Imagery and copy are usually free. Write that down somewhere people will see it.
Review the output, not the process
Look at what actually got published each month. Drift shows up in real assets long before anyone reports a problem.