What is clear is that at this time Mane position is still irreplaceable, Diaz and Nunez are still beyond expectations, that Liverpool still need aggressive players and have attacking instincts as well as being proficient in assists. Look at Nunez performance at the World Cup, just as he can't give his best. It still takes time for Nunez maybe 2 to 3 years he will be greater. But for now Liverpool needs a new player who can collaborate with Moh Salah on the front lines. Because Liverpool's attack structure is still ineffective.
Firstly, Nunez is a striker while Mane is a winger. I mean the natural positions of course. Otherwise I know that Mane can play as a centre-forward sometimes if needed. Nunez started the season really poorly but he improved his performance later on at Liverpool at least. He started to be more effective in scoring goals. He was signed for 80m in the end so he is under pressure to perform decently as the expectations are big. The reason why expectations are big is obviously his amazing performance at Benfica before.
When it comes to Diaz, I think that he is doing just fine now. He is the closest player to Mane in terms of playing style when we compare Diaz and Nunez for this. Diaz is very helpful in attacks and he is taking a big responsibility in scoring great goals for Liverpool also. There have been many times he made things easier for Liverpool while they were in some trouble. He has had an unfortunate injury later but he is expected to return at the end of the month.
Liverpool have the needed kind of players to be effective in attacking in fact. They just need to improve their mental and it will be enough for them to start winning as usual.