Liverpool has a great team, and I agree with you that Liverpool doesn't need to do much in the transfer window since they have a good squad that can compete in the UEFA Champions League competition and the Premier League or any other competitions they will play next season.
If Liverpool starts next season with this squad, they will not be able to defend their premier league title they just won because they are very lucky last season not to have injuries, so they need more squad depth this coming season so that they can deploy some players when their main key players get injured.
Trent Alexander Arnold left the club for Real Madrid, they need to replace him, and also need more depth, but since they have signed Writz from Leverkusen, they have improve their attacking line, they will also need a striker because Nunez is not reliable. If they can get more players, they will be good to go.
I agree with everything that you said. Liverpool was lucky last season because the players were injury free. They need to sign more players to replace any player that is injured or drop form next season. TTA needs to be replaced with a player that has similar strength and quality like him. It might be difficult for Liverpool to defend the title next season.