Mosaic outputs clean, semantic code and can absolutely be SEO friendly, but you need to use the given features, to get the best result.
Images
At Image elements always use their Alt field to describe the content of the image.

Headings and text
Use Heading, Text, and Paragraph elements logically to create a clear structure.
- Headings should be used as titles and subtitles.
- Text elements can be used for short standalone content.
- Paragraph elements are intended for longer descriptive text.
Meta tags
For page titles, descriptions, and other metadata, use an SEO plugin like Yoast SEO, which works seamlessly with Mosaic.
Optimization
Website speed affects search engine rankings. To achieve the best results, ensure your website is optimized, as you see in the speed optimization documentation.