It’s not really a film-vs-digital difference. The effect you’re seeing comes from the viewfinder’s focusing aid.

Older manual-focus cameras often use a split-prism focusing screen. When the lens is out of focus, the image appears split into misaligned halves; when focus is correct, the halves line up. This was designed to make manual focusing easier.

Many newer cameras, especially autofocus SLRs and DSLRs, use plain focusing screens instead, so out-of-focus subjects look uniformly blurry rather than split. Once autofocus became common, split prisms were less necessary, and camera designs also had to direct light to AF sensors. That can make split-prism screens less practical and more prone to darkening or blacking out.

So the difference is mainly due to the focusing screen and focusing system, not whether the camera records on film or digitally. Some film cameras have no split prism, and some digital cameras can use one, including certain manual-focus models or aftermarket screens for DSLRs.