At least after Manchester United victory in the Premier League against Everton it certainly increased the players confidence to try their best against Galatasaray. However, that alone was not enough because Galatasaray squad was solid, mature and able to move to create opportunities to fully support victory. Moreover, this season Manchester United chances in the Champions League are quite slim, we'll see if they succeed in beating Galatasaray it means increasing their chances of improving in their last match. Personally, I would bet that Galatasaray playing at home will provide positive motivation.
Manchester United's victory at the Goodison Park during the last weekend without doubt is gonna boost the team's confidence and morale going in their fifth game in the UEFA Champions League competition which is an away match at home of Turkish Super Lig champion Galatasaray. But likely you rightly pointed out, that doesn't guarantee them of a win against Galatasaray later tonight because just the Turkish club has been more formidable than their visitors in the UCL this season as well as has performed better in their league than what Manchester United did in the English Premier League.
Considering the general impressive performance of Galatasaray this season, I'll be very surprised to see them suffer a defeat against United tonight knowing how important the game is to them as a team.
On paper, Man United can beat Galatasaray even though they act as the visiting team. I say that because I see United as an elite club in the EPL, and have been poor in the UCL, even though I understand that the Ten Hag squad is currently the club most highlighted due to their poor performance, no longer because of their good reputation. This doesn't mean I underestimate Galatasaray, I never thought about that at all, because I still remember how Icardi and his colleagues beat United in front of their supporters in the first leg.
Apart from that, Bayern is now in a safe position which will certainly reduce the tension of the game a little, this means that Copenhagen will maximize their efforts to record a draw, because beating Bayern can be said to require a miracle. If Bayern and Copenhagen draw, and United and Galatasaray draw, then the Danish representatives will have the luck to qualify for the round of 16, even though they have to fight again in the deciding round in the last match against Galatasaray.
I think the situation for group A is quite complicated in fighting for one slot to the next stage, it could be that the prediction goes according to the circumstances and could be completely wrong. I really understand that the UCL is very different from domestic competitions, it requires mentality, hard work and teamwork to progress step by step, although sometimes luck will play its role and side with an unexpected club later.