GCG and type 2 diabetes mellitus: T2DM: Type 2 Diabetes Mellitus; BMI: Body Mass Index; RYGB: Roux-en-Y Gastric Bypass; SG: Sleeve Gastrectomy; GLP-1 RA: Glucagon-Like Peptide-1 Receptor Agonist; SGLT2i: Sodium-Glucose Co-Transporter-2 Inhibitor; FGF19: Fibroblast Growth Factor 19; GIP: Glucose-Dependent Insulinotropic Polypeptide; QoL: Quality of Life; FPG: Fasting Plasma Glucose; UAE: Urinary Albumin Excretion; DKD: Diabetic Kidney Disease; HRQoL: Health-Related Quality of Life; PTH: Parathyroid Hormone; CTX: C-Terminal Telopeptide; OC: Osteocalcin