Here are two ideas that are simple and would help give the effect.

You already have a semi secret garden in the lawn area where the birdbath is. Heighten that effect with a 5' hedge or bushes starting on the right of the front walk so you don't see that area until you enter the front walk.

You don't want hedges blocking the view to the front door. Clear an area next to the front porch for stepping stones for a wandering path as a shortcut to the front. This will draw the eye down to the lawn and create an illusion of intimacy.

I don't have software but here is a sketch to show concept.

I can't tell what plants you have there, but if they will grow taller, just be patient. If everything you have planted will stay small, that won't create what you want. You seem to have the right idea in the area near the bird bath, so just build on that everywhere.

I love these ideas!! 🥰

Use hedges, tall grasses, or layered plantings to divide the space subtly:

Boxwood or yew hedges work well for structure.

Ornamental grasses (like miscanthus or calamagrostis) can add texture and seasonal movement.

Let flowering shrubs like hydrangea, viburnum, or roses grow densely to create natural walls.

Some option:

Are you talking about just the lawn area? Because I'm curious if you could use the areas beyond the rocks, down the stepping stone path, the end of the access road. You don't show those areas, but all of those areas seem separated and somwhat private and could be turned into rooms.

Here is another view of the house. There's a right and left lawn with a walkway down the middle. At the far end (right side of picture) there's a small curved garden bed that lines around the grass but ends there. I feel like I'm limited and the cedar lakehouse doesn't lend itself well to the secret garden look the way that a stone house would. I'm adding 2 arbors which will hopefully help. Thanks for the suggestions and I'm open to any other feedback of course.

All good advice above. It will take time for plants to achieve enough fullness to be used as walls or barriers to create rooms. I do like your idea of salvaged elements to also create rooms.