All?Strangely, people saying all the signings that have continued were signed by the club and not him. How do you know? It is a stupid thing to say as you could selectively say that about any signing. I could say that about Fernandes without any real evidence. Like it or not, they were signed whilst Mourinho was manager. It seems people only want to attribute the not so successful parts e.g. no credit for Pogba but get the blame for Mkhitaryan - who actually contributed quite a lot to the Europa League victory.
That's too overstretching.
You know how the system of players joining and leaving but more so buying players at United works right? albeit it's unique at first i.e. "traditionally" highly dependent on manager but now it's changing. I think the "transition" started during LVG's first season. The "situation" or management then is a mess but finally getting into proper form in Mou's second season I believe.
Fact is there were recent reports finally detailing how the negotiation/discussion of players system are being handled within the club, and no, not just one person that decide all. The system they used is somewhat similar to majority rules or something. It's possible that the manager may not push for certain players but the players can still be bought. From this, we can make inference of connections with the players that were being brought in during LVG, Mou and Ole.
I think the club signed only three -- Fred, Grant and Sanchez. Mou is not against them. Meaning, the club scouts and the other internal people in charge were the one that recommended and push the deal to get them. Mou didn't made any specific requests nor play active roles in getting them. Grant is arguably a "player" with specific criteria which Mou requested in response to Romero's injury and to also allow the other youth keepers continue on loan which the club get him for because it's cheap and aligned with the youth philosophy. Basically club signings is when Mou being passive in getting them.
The other players like Pogba, Bailly, Zlatan, Mkhi and the rest are definitely Mou's signings because he play active roles in getting them all. There were good reliable reports of Mou contacting Pogba and Zlatan personally to convince him (if I recall the players themselves revealed it), he also watched Bailly, Dalot and Lindelof play in their respective leagues, and Mkhi is similar to Pog and Zlat -- all three are the voted best players in their leagues before joining. All those are also Mou's typical type of players.
Another speculation for me is that Bruno is not Ole's signing, moreso he's the club's signing but Ole is not against getting him. I think the club scouts (and the others) recommended to get Bruno early season 2019/20 but they may decided to give faith to Lingard so no deal... yet since the situation kept on getting worse, getting Bruno became an urgent in Jan. The other three is Ole's (direct) signing. Ighalo is similarly Ole's request and the club get him that player who fits the profile.