Deciding to wait for Mbappe to be free is difficult now because by extending Mbappe's contract for 1 season indirectly this makes PSG still comfortable with selling Mbappe at a fairly high price.
Now indeed the decision is in Madrid whether they want or not to spend money on Mbappe especially I think for now they (Madrid) can be more comfortable to negotiate because Mbappe will definitely be sold in the summer because PSG has no choice now apart from selling Mbappe because the way of coercion they cannot do for a player of Mbappe's calibre.
PSG will not sell Mbappé for a high price, even if they extend the contract for another year. Mbappé seems to have determined that his next stop will be Madrid. He turned down many offers from big clubs. Continuing to prolong this transfer will cause damage to both sides, but the one who will suffer the most is probably PSG. They could lose Mbappé entirely without getting any money.
That's right, Madrid is the beneficiary, and PSG has to sell Mbappé to them at a cheap price. Madrid is the one who decides. They can buy Mbappé, and Haaland is also a suitable name for them to spend money on. If PSG keeps the transfer price tight, Madrid is ready to find another player.