Is there a way to substitute the nuts or nut butter in recipes?

Well, potential replacements will more than likely depend on the specific recipe. Or in some cases it can even be omitted entirely without substitutions.

If you give concrete examples, we might be able to make suggestions?

Unless you like seeds, like sunflower or pumpkin seeds, I don't have direct suggestions.

But I agree that in most cases they can be left out. If you want crunch, in savory dishes you could consider something like dry-roasted soybeans, crispy chickpeas, croutons, or a crispy vegetable. If you want something in sweets, consider dried fruit bits (but you may need a bit ore water or other fluid in the recipe).

If you're baking, nut butters in the recipe are adding some oil and some solids. If you experiment, you can probably figure out a rational adjustment for such recipes. If you look at how many grams of fats are in the the amount of nut butter the recipe calls for, that'll give you a hint about how much extra oil to add. How much extra solids to add, and what type, is more complicated - could be some type of grain product (flour, groats, flakes, whatever).

Whole or coarsely chopped nuts in baked goods don't usually add much oil to the recipe. You might need a bit extra, but mostly you should just be able to leave them out.