The thermic effect of food (TEF), also called diet-induced thermogenesis, is the rise in energy expenditure after eating as your body digests, absorbs, and stores nutrients. On a typical mixed diet it accounts for roughly 10% of total daily energy expenditure, making it the smallest of the main components alongside resting metabolic rate and physical activity. It differs by macronutrient: protein costs the most to process (roughly 20–30% of its calories), carbohydrates less (about 5–10%), and fat the least (about 0–3%) (Westerterp, Nutrition & Metabolism, 2004 (external link)).
On a GLP-1, eating less food means TEF shrinks along with intake, which is one small part of why calorie burn drops during weight loss. Keeping protein high helps a little here, although its bigger payoffs are fullness and protecting muscle. See calories in, calories out and do TDEE calculators still work after big weight loss?.