My sleep apnea started in my mid 20’s when I weighed 155 pounds, very low body fat and very athletic. I was a pilot rescue swimmer, competed surfing, played soccer competitively, ran every day, lifted weights, etc.
The apnea was undiagnosed for 25 years and pretty much destroyed my health. I did gain weight the last 7-8 years of those 25 years due to the inability to maintain any energy level.
The condition can lay the mighty very low and kills people early. Being overweight does make it worse in some, but many have it bad and then become overweight.