I think it is incorrect to say Ole has no system. Based on the following.
Against weaker teams Ole's tactic is to use Pogba and Bruno to play probing forward passes to Rashford-Martial-Greenwood repetitively until a defensive mistake is forced, hence our incredibly high number of penalties. Once a lead is established, United can then allow the opposition onto them and hope to break at pace again using Bruno, Rashford, Martial, Greenwood's speed and pick off opponents. Matic is perfect as a covering DM due to his physical presence and QB style passing range. Bruno was specifically chosen as a priority signing because of his willingness to force forward passes, even in situations where he might lose the ball. Its a matter of risk v reward.
Against stronger teams, Ole's tactic is to sit deep, invite pressure and then release our pacy forwards on the break. In these games he also tends to opt for more legs in midfield and may use McTominay ahead of Matic or Fred ahead of Pogba. If a lead is taken United can again sit back and look to pick off oponents on the break.
What I don't understand about this tactic though is his insistence on using Lindelof and Maguire in a high line, weaker teams with fast forwards exploit this again and again against us. I actually don't mind Lindelof as a player, I think he is decent on the ball and as a ball playing CB I actually prefer him to Maguire in that role. The problem is that he is completely useless 1vs1. Maguire is capable 1vs1 but only against large target men strikers. He gets beaten for pace all the time and looks embarrassingly bad when doing it. I understand that AWB was bought because of his ability to recover and sweep up behind these 2. However, I think it is painfully obvious that AWB can't cover for both of them and a pacy hard hitting defender needs to be bought to play alongside Maguire or Lindelof. I wonder if Ole thought Bailly or Tuanzebe would be this partner for Maguire but just hasn't developed. Maybe Mengi can be that guy, otherwise we need to invest in a pacy commanding CB. I don't have a huge amount of ideas for this option but I know Alaba is trying to force a move away from Bayern, there is talk of Koulibaly but he would be incredibly expensive. Funnily enough, if we had not signed Maguire, Soyuncu would probably be a better partner for Lindelof.