Barcelona will certainly make improvements to their team considering that the matches for next season will be even more difficult. Each team will certainly try to have better performance than before so they will train harder. If Barcelona wants to win it, they have to start now and maybe there will be a change in strategy later if it is needed. Barcelona also needs to lighten their financial burden by selling some of their players so they can have better players.
Change is needed in every competition but I think Barcelona doesn't need to make changes for now because I think their squad is perfect enough to compete next season, Hansi Flick just needs to maintain what he did last season, but maybe the small shortcomings that need to be fixed are on the defense side because even though their defense is not bad sometimes the players like to make mistakes that result in defeat.
Btw I haven't heard the latest news regarding the purchase of Nico, has Barcelona not found common ground with Athletic Bilbao?