Ok, now the match can go on.
Unfortunately we don't know much about Darkseid, due his nature as a dlc, and afaik the comics don't go much in detail either, so we'll have to work with what we have.
Going by numbers, Evil Ryu is already 4.5x times stronger than Darkseid, although he lacks in LS.
Evil Ryu is most likely the better fighter of the two, and has arguably better mobility between his acrobatics and the Ashura Senku.
Darkseid would probably lose ground in cqc, especially if his tendency to take the opponent lightly comes into play, but can instead get the advantage in ranged combat.
Omega Beams are nasty, since they outrange Evil Ryu's hadokens and can home in, likely interfering with Evil Ryu's mobility and possibly yeet him into space, unless Darkseid pulls the moronic move to bring him back to Earth with a boom tube.
Due to their strength, Evil Ryu's hadokens can't be overpowered by the Omega Beams, which can still circle around them. Still, were Darkseid to be hit, he'd suffer major damage not only because of their raw power, but also because of their great heat.
As said, the SGS would be an absolute instant kill, but it needs to reach Darkseid first. Ryu's greater mobility would definitely help, unless Darkseid spams Omega Beams, but admittedly Evil Ryu can spam Ashura Senku as well and pass through the beams, forcing Darkseid to either maintain the defensive or keep escaping through Boom Tubes. Also, how fun would it be to see Evil Ryu undergroundmobilitin' his way through avoid the Beams?
Darkseid can fly, which could furtherly help him, but I don't know how in-character it is for him. Evil Ryu can somewhat keep up with ranged attackss, acrobatics and his ability to jump very high, but it has clear limitations.
Overall, I vote Evil Ryu, since he most likely has better chances, although Darkseid could still prove his worth and win if he fights in a certain way.