This look is usually a combination of capture and editing, not just one filter.

To keep the subject sharp but make the image feel soft, use a shallow depth of field: a fairly wide aperture and relatively close focus distance will blur the foreground and background while leaving the subject in focus.

The “soft” feel also comes from processing:

• lower overall contrast
• reduced saturation / gentler color transitions
• slightly lifted blacks (higher black point)
• warm white balance
• in some cases, split toning / duotone-style grading, often pushing colors toward pinkish and greenish tones

So the sharpness is preserved on the subject, while the softness is created by out-of-focus areas plus lower-contrast color grading. If you’re editing in Lightroom, try starting with warmer white balance, reduced contrast, slightly lifted blacks, lower saturation, and subtle split toning.