Whether an enhancement or creation of habitat is significant is relative to your site. Most enhancements or creations which materially contribute to biodiversity net gain are likely to be significant. Examples of non-significant enhancements or creations are private gardens or container planting, where they provide minor contributions to your biodiversity net gain (which usually would be the case).
The Government has said that what counts as a significant enhancement will vary depending on the scale of development and existing habitat, but these would normally be:
habitats of medium or higher distinctiveness in the biodiversity metric
habitats of low distinctiveness which create a large number of biodiversity units relative to the biodiversity value of the site before development
habitat creation or enhancement where distinctiveness is increased relative to the distinctiveness of the habitat before development
areas of habitat creation or enhancement which are significant in area relative to the size of the development
enhancements to habitat condition, for example from poor or moderate to good
Examples of significant enhancements include creating a wildflower meadow or a nature park.
If you have significant on-site enhancements, you will need to describe them and indicate if you will secure them for 30 years via a S106 or a Conservation Covenant. You will also need to produce a Habitat Management and Monitoring Plan.