At the end of the day, there's just not a lot of energy in human waste. Poop is what's left after your body has extract all the energy it can from food.
I don't think energy recovery from sewage is feasible, not in the short term, not with our current infrastructure. But either way we should be treating our waste more deferentially in an attempt to recover the minerals 6 billion people poop every day. Except for water, everything in pee and poop is valuable if recovered (urea ->energy, phosphate ->mineral, sulphur ->mineral, starch ->energy)
Instead it all gets dumped to the oceans and the ocean dies from too much nutrients
Animal manure is very good for plants and many gardeners seek out chicken, horse or cow manure.