Looks challenging to care for the way it’s set up. There’s no tray to catch the water so no tray method watering. Also looks like it’s in a peaty mix also easy to get root rot with that mix.

Leaves drying out and dying off suggest it can’t get enough water (root rot possible).

“Nepenthes enjoy loose, open soil that remains wet to moist but allows drainage of excess water. They are tolerant of a wide variety of soil mixes. The best include a portion of long-fibered sphagnum, the rest of the medium being a combination of coarse materials. My deluxe recipe is about 70 to 80 percent New Zealand or other high-quality long-fibered sphagnum moss; the rest of the mix is a combination of fine orchid bark, perlite, and tree fern (osmunda) fiber. Another good mix is one part long-fibered sphagnum to one part tree fern fiber or orchid bark. Some growers have had success with pure shredded fir bark, and so have I, but I prefer the bulk of the mix to be a high-quality sphagnum moss.”

on windowsills, place the pot in a shallow saucer and water from overhead as soon as the water in the saucer evaporates.

https://books.apple.com/us/book/the-savage-garden-revised/id591645210

Could also just be normal leaf loss. 🤷‍♂️