I don't think we will go for him.
Our bosses are fighting heavily for a contract extension of Alaba. If he stays, the left CB spot will basically be occupied for the next years.
Then we have our record transfer Lucas Hernandez. A pairing of Alaba and Lucas isn't going to happen. We wouldn't stand a chance against big and strong attackers and the built up play wouldn't be ideal with two left footed CBs.
As you saw against Barca, Davies will surely stay left full back, meaning that Lucas Hernandez might (and should in my opinion) be sold.
Regarding the position of the right CB. Under Flick Boateng experienced his second spring but he's not as good as in his prime. Once Süle is completely fit, Boateng will be benched. It wouldn't surprise me, if Süle starts against Lyon.
Additionally we got Tanguy Kouassi Nianzou from PSG (by the way he said he prefers Nianzou over Kouassi which he used at PSG) and we obviously convinced him that he would be given more game time in Munich than in Paris even with Thiago Silva retiring.
On top of that we have Pavard who mostly played as a right back for us, but also can play CB.
So, for now we have as CBs: Alaba, Süle, Hernandez, Boateng, Nianzou, Pavard, Martinez.
Martinez is as good as gone, but even then we have more than enough options for the right CB.
I can imagine that we sell Lucas and buy a "cheaper version" of him respectively a "Pavard for the left side" , meaning a backup for left CB and left full.
And, as Flick showed that he gives youth players a chance, we have the 17 years old Bright Arrey-Mbi, that is very highly rated by everyone in the club.
tl;dr: Even if Boateng and Lucas leave until next summer, I cannot imagine us going for Upamecano, because for the position of right CB we have Süle (basically the German version of Upamecano), Nianzoud, Pavard and Arrey-Mbi.