I don't think Mbappe will ever be on Barcelona's radar. Currently, the Blaugrana almost have a mature squad with unstable financial conditions. I think the arrival of Gundogan is enough to complete the Barca squad to return to control of La Liga. Osimhen could be the right option if Xavi wants to add strength to his attack line, but the price is too high, of course the team from Catalan cannot afford it.
Players are valued and some are undervalued, with accordance to their performances. The blaugrana have no ambitions to sign Kylian Mbappe, who has been linked with Real Madrid for specific time, or Victor Osimhen. We are talking about players whose demands are greater and more valued in the transfer market, and Barcà has not offered to sign them, even if they would if their financial situation was better balanced. This summer, Barcelona added several good players, including IIkay Gundogan, who would strengthen the midfield for Xavi Hernandez, a fantastic structure for the club.
Barcelona managed to sign Gundogan because Gundogan is also on a free transfer and also, even though Mbappe has been linked with Real Madrid for a long time it is also not a guarantee that Mbappe will go to Real Madrid. So yes, anything can still happen and "for example" Mbappe to Barcelona, it is also still possible to happen. But unfortunately, Barcelona do not have stable finances in this moment and of course, with financial management that is not good then it makes Barcelona at this moment do not have big plans to bring in the most expensive players.