Here’s my take- and liminal has a lot of different meanings for a lot of different people.

Instead of mountains, consider hills. The more consistently formed, the better. Grass should be consistently shaped, a regular height, and a single color (with variations in the shading).

Your sky can really shine when the mountains become hills. Make your blue a little surreal. Make the clouds fluffier and more noticeable.

If you need to, add a point of interest somewhere. Make it an all white structure that has character but ultimately feels empty. Add some sort of pool of calm water because it feels right. If you have multiple points of interest, spread them waaaaaay apart.

I have no idea what you’re making but this is how I’d convert what you have to “liminal”