Not buying any of them are better than TAA or Carvajal or Walker as all around players.
I think I would take Canelo in and Semedo out--but it must it would have its risks or Juv wouldn't be wanting to move on from him, or we give Semedo another year to cement his place. Either way I don't think RB is a prime area of need, it is only an opp if there is the right great player out there. It was Jordi Alba more than anyone ended our season. Get someone like Felipe Luis to give Alba more of a rest and a little more tougher character defensively when we need to better grind a lead, and I our full backs are settled.
Wait a second, who mentioned anything about Cancelo or anyone else for that matter, being the best overall right back? In any case, I don't think that either of those 3 that you mentioned are better offensively than Cancelo. Maybe with the exception of Trent Alexander-Arnold.
The RB position is not the most pressing need but if we could replace either of Semedo or Roberto with a better player with minimal costs, I would obviously not be against it.
You seem to agree if replacing Semedo with Cancelo was an option.
Likewise I would part ways with Umtiti in an instance and pay the extra to get de Lift in return. Likewise sell Coutinho and pay that little extra to get Griezmann. Rather than stupidly chasing Neymar.
In an ideal world I would get rid of either Rakitic or Busquets (Rakitic more likely and easier to replace) and buy another midfielder as well in the mould of Fabián Ruiz or Kai Havertz.