I read it quite a while back but I cant find a single bookmark for it. MC transmigrates into a fat guy who has been sent to the "old home" away from the capital because he embarrassed the family when he hit on some important guy(who liked his brother). He builds better charcoal, glass, grenades and a whole bunch of stuff. He ends up with the adoptive father of the guy his host hit on, ML is "god of war". He adopts some kids and teaches them, women/girls too. Help!
I was thinking to find it from @purple_mangosteen's list but its not there.... https://forum.novelupdates.com/threads/bl-shonen-ai-yaoi-novels-recs.84327/
more details i remember; mc also produces sugar, here is a part where he saves a slave who is a foreigner(blonde, blue eyed who ends up being a prince and he eventually gets ML to convince emperor to help him take back his throne. First time mc and ml meet is when ml was injured and was being chased and mc ends up faking that ml was a pretty guy that he was bedding...his rep was that bad at that point and ml was supposed to be super hot. one of ml's entourage was a doc that told mc that his weight was coz of his step mom medicating him.
Sorry, Its been forever since I read this and all the bookmarks I had from that site and 88danmei are dead links. I'll put this post back up.