That depends on if your edits add anything that is unique to the native Affinity file format. For example, I added a rounded rectangle to a simple one layer tiff format file, so it now has 2 layers. When I click "Save" I get this notice:
The first option, "Save with layers," saves the file in tiff format, but adds a private tag that 'tags' that added layer as an Affinity rounded rectangle shape. Affinity apps read that tag so if you open the tiff file saved with that option the layer will still be a rounded rectangle shape. Other apps ignore the private Affinity tag & just treat it as an ordinary shape or part of a single layer raster image, depending on their capabilities. "Save As" saves a new version of the file in the native Affinity file format.
Siegfried got a reaction from MEB in tiff opened as raw