Most likely in the first leg, Roma strategy will focus more on the defense line, at least being able to bring home one point from Porto is a good result, although it will be quite difficult because playing in front of the opposing team supporters will at least affect the players mentality. On the other hand, of course Porto doesn't want that to happen, so winning at home will be the price they have to pay. In terms of chances, I see both teams have an equally big chance of qualifying for R16, but it also depends on how prepared and serious they are in playing these two legs.
Referring to what you said, usually Roma will only aim for a draw when playing away in the Europa League competition. This scenario could happen again, assuming that you said that Roma is most likely focused on aiming for one point for the first leg. but that doesn't mean they are not focused on winning, because full points in the first leg will mean a lot to them. although it seems like it's not an easy job, especially since Roma's performance is far from stable in every match. a job that is not easy for Ranieri, even Artem Dovbyk who they brought in last summer's window has not answered the team's needs in AS Roma's front line. in the Porto camp, Roma is actually one level better than Porto in the Europa League qualification table. but in this meeting it seems that Porto will be much more pressing to score three points and maybe try to score a lot of goals, although Roma will not let it go easily. both teams have the same chances, but Porto is favored in the home game. it could be as you said, in the meeting between the two teams Roma will focus more on defense, with the scenario of making a quick counterattack. let's see, which team will benefit and win this match. by the way, I doubt if this match will offer an exciting and much more interesting match.