General

yes, I think this is a very common issue for a lot of men who get fat. I notice the bigger I get the harder it is to get hard, although, my age could also be a factor.

Depending on your age, testosterone does dwindle as you get older.
With that, libido declines as well as firmness and length of erection time.
Happens to us all.
Methods to improve it would be to enjoy yourself when you have a lot of energy as opposed when you are dead-tired.
Further, taking up low-impact cardio can help improve heart-health. Low impact will burn fewer calories and preserve joint health. Meaning, better blood flow below your waistline without worry about weight loss. Good luck.

If you are struggling to get hard, please see a doctor as that may be a sign of cardiovascular issues.

Same with me...not able to get hard enough for long enough to penetrate anything now lol

The good news is that low testosterone is treatable. It's not unusual for obese men to have a hormone imbalance and have low testosterone. There are creams, lotions, pills, etc.

I know a lot of men will ignore this sort of thing and try to get by. Don't ignore it. Struggling to keep or maintain an erection isn't a mark against your manhood, but it is still a medical concern.