I think Barcelona will have to wait until the end of this season to sign new players. It's hard to find good players right now. Each player is currently under contract with different clubs. Nowadays, to think about new players for Barcelona, a lot of money is needed which Barcelona does not have at the moment. As you said, Barcelona have not been able to sign top quality players in recent years due to the club's current financial crisis. But many are not willing to accept these things. These things many people without trying to understand, are blaming Xavi and expressing their displeasure with a coach as skilled as Xavi.
Even though Robert Lewandowski can be said to be a new player at Barcelona, in reality his presence brought victory only at the start, whereas currently conditions cannot bring victory to Barcelona, even though he scored a goal in the 33rd minute, which shows that Robert Lewandowski is still trying hard to score goals even though Barcelona is experiencing quite critical internal problems.
He has already had one season with Barcelona and this is his second season with Barcelona so he is not a new player anymore. In his first season, he successfully led Barcelona to become champions and was also the top scorer last season. but this season he was not able to maintain his best performance and there were also several big obstacles, including he also suffered an injury this season. I think he is old and it is very natural that his performance has decreased.
Xavi must immediately prepare a more impressive, younger striker to replace Lewandowksi if one day Lewandowski is injured. Apart from that, Barcelona is still quite strong this season because they have quality players in their team such as Lewandokwsi, Gundogan and also De Jong. Xavi must transition more young players into his squad.