The latest rumors are that Joselu will soon go to Qatar. Even though Real Madrid has finalized an agreement regarding Joselu with Espanyol but, it looks like Real Madrid will release Joselu to Al Gharafa at Joselu's own request. Maybe Joselu really realizes that he wants a lot of playing time then he won't get it at Real Madrid. Another consideration is that he will clearly get a bigger salary and I think that is a realistic thing for players who are entering their retirement period.
In my opinion, why Joselu would rather move to Qatar than accept a contract extension from Real Madrid is because of the duration of the contract. Joselu will receive a contract for 3 seasons in Qatar while at Real Madrid it is rumored to be only 1 season. As a player who is 34 years old he certainly needs certainty to be able to play longer by accepting a longer contract, especially if he has not thought about retiring within the next season or two, also the money he has earned so far is not yet fairly large, and looking at the list of clubs he has defended I guess he is not a player who receives large payments, because besides Real Madrid the other clubs are just average clubs not elite clubs.
The presence of Mbappe could be his consideration because will make him even more forgotten because he may only play at certain times, for example when Real Madrid's main players are not fit or when the match results are not important.