Hypogonadism: Given the patient's symptoms of low libido, fatigue, and muscle weakness, along with the use of finasteride (which can contribute to hypogonadism), this diagnosis is highly plausible. The patient's age and lack of exercise could also contribute to decreased testosterone levels.

Sleep Disorder (e.g., Hypersomnia, Sleep Apnea): The patient's ability to sleep for days at a time and excessive daytime sleepiness despite sleeping a lot suggest a sleep disorder. The use of Adderall XR, a stimulant, and high caffeine intake to combat fatigue also points towards a sleep disorder.
Depression: The patient's symptoms of brain fog, fatigue, and low libido, along with the prescription of Trintellix (an antidepressant), suggest that depression could be a contributing factor to his symptoms.
Anemia or Iron Deficiency: Fatigue, weakness, and brain fog are common symptoms of anemia or iron deficiency. Although not directly indicated, it's a common enough condition to consider, especially given the patient's lack of exercise and potential poor diet.
Thyroid Dysfunction: Hypothyroidism can cause fatigue, muscle weakness, and brain fog. Given the patient's age and symptoms, thyroid function should be evaluated.

Adrenal Insufficiency: Although less common, adrenal insufficiency can cause fatigue, weakness, and low libido. Given the patient's use of stimulants (Adderall XR) and high caffeine intake, which could mask some symptoms, this diagnosis should not be overlooked.
Pituitary Tumor or Hypopituitarism: A pituitary tumor or hypopituitarism can lead to hypogonadism, thyroid dysfunction, and adrenal insufficiency, causing the patient's symptoms. This is a critical diagnosis not to miss due to its potential for serious complications if left untreated.
Sleep Apnea with Associated Cardiovascular Risks: Given the patient's age, weight, and lack of exercise, sleep apnea with associated cardiovascular risks (e.g., hypertension, heart disease) is a critical diagnosis to consider and rule out.

Chronic Fatigue Syndrome/Myalgic Encephalomyelitis: This condition is characterized by extreme fatigue that cannot be explained by any underlying medical condition. It's a diagnosis of exclusion and should be considered if other diagnoses are ruled out.
Mitochondrial Myopathies: These are a group of disorders caused by mitochondrial dysfunction, leading to muscle weakness and fatigue. They are rare and typically present with more specific muscle symptoms, but could be considered in the differential diagnosis if other causes are excluded.
Prader-Willi Syndrome: Although extremely rare and typically diagnosed in childhood, Prader-Willi Syndrome can cause hypogonadism, excessive daytime sleepiness, and muscle weakness. It's an unlikely diagnosis but should be considered if the patient has a history suggestive of this condition.