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?
Nico's situation with Bilbao, especially with the fans, is still quite tense now and it seems that this can still be used as an option for Barcelona if they really want Nico at the Camp Nou for next season. It's just that this is also still a little complicated because we must be aware that even though they won the trophy last season and of course there were bonuses they earned but it still couldn't make their financial condition change to be fine.
This needs to be considered so as not to let the ambition to bring Nico to Camp Nou actually make the same situation as what happened to Dani Olmo last season. Moreover, for now I quite agree with what you say where they actually still don't need to do an overhaul but if they still want to do it then no problem, just don't let this burden them in terms of conditions and finances of course.