Liverpool have already proven that they are the strongest team in the Champions League. Liverpool have won all 7 matches and are at the top of the table. The match against PSV is not important for Liverpool. Even if they lose this match, Liverpool will still be at the top of the points table.
I doubt very much whether Liverpool will give their full effort in this match. Because the next two matches are even more important for Liverpool. Liverpool will play against Bournemouth in the Premier League match. Bournemouth is in great form at the moment. And in the next match, Liverpool will face Tottenham in the semi-finals of the EFL Cup. So I will not be surprised if Liverpool does not give their full effort in the match against PSV.
In the 8th UCL match, Liverpool may not play their main players full time. It is possible that there will be a rotation of players and give playing opportunities to second tier players who need experience playing in the UCL. So I also wouldn't be surprised if Liverpool didn't get maximum results in the 8th match, namely against PSV.
Meanwhile, PSV really needs a win in the match against Liverpool. Because PSV is not yet in a safe position to qualify for the Play-off round. They must secure full points or a draw to get a ticket to the play-off round.
You are right. Since the match is not important for Liverpool. So Liverpool may not play with their best XI in this match. Liverpool may rest some important players in their squad. Liverpool has a very busy schedule this season. So if they want to maintain consistent performance, they should definitely rest the players in less important matches. Otherwise, the risk of injury increases.
The match is very important for PSV. The team is in 19th place in the points table. Qualifying for the playoffs is still uncertain. The team has scored 11 points in 7 matches. So the match against Liverpool is very important for PSV. PSV needs to score points in this match if they want to qualify for the next round.