If your lentils are still crunchy after 30 minutes, don’t panic. First, check your water level. If it’s all absorbed, add more hot water. Lentils are thirsty little sponges. Second, you might have old lentils. Yup, lentils from the back of your pantry from 2019 are going to take longer. They lose moisture over time. It’s not you, it’s them.
Lentil Cooking Times by Color | Lentils dry to cooked weight conversion
Also, hard water can slow things down. If you live in an area with mineral-heavy water, use filtered water or add a pinch of baking soda. That’s a hack your grandma probably knows. My grandma used it, and she was never wrong.