I still think that Kane was a terrible transfer by Madrid, sure he has been good at premier league for a while but he is old, and thinking that they can do well enough and I mean like not amazing, just well enough for them that is fine. However, they really needed someone that would take them to the top spot.
By comparison, let me tell you this, they wanted Mbappe before his huge deal with PSG, they offered like 150+ million for him, nearly 200 with the bonuses and such, do you really think that's fine? I do not think that Kane and Mbappe could be even comparison, they really wanted a superstar and instead they have said enough with shell of a past success guy. In any case, if it's true and if he signs the deal, that's a terrible decision for Madrid without a doubt.
What source are you citing here? Kane hasn't agreed to anything and officially is still a player of Tottenham Hotspurs. How do you know that he transferred to Real Madrid? If I am informed correctly, Real Madrid made a first offer after Benzema let the club know that he is going to leave this summer, but nothing has been signed yet. Benzema leaving the club makes it more likely though that Real Madrid will now see whether they can find an appropriate substitute and it seems they are offering 100 million pounds, which I think is too much for Kane given how old he is.
In the case of Mbappe I think that Real Madrid now has Vinicius Junior and they are very satisfied with him. They actually play the same position and one of them would have had to switch sides then.