Dont judge the goal keeper yet because you watched a compilation of his mistakes as a GK. Every player has their best and worst moments in football. This shouldn't be what the fans should focus on.
I also watched the video and my conclusion is this, he may not be what Manchester United want at the end of the day but I am sure he is better than Andre Onana.
I am not actually judging the new goalie, but I must confess that such a video is very demoralizing. If by mistake he eventually stumbles on that video, it will negatively impact his performance.
Don't you know that media is one of the reasons Onana failed in Manchester United? And each time he tries to pick himself up, he will be bantered by the media. It is not all players that wins the war against media. It is only Onana that successfully dealt with it.
So, it will not end well if media starts their negative energy campaign against Lammens
By now he must have watched that video a couple times. If the video influences his performance in Manchester United poorly, I guess he is not a professional goalie and is not qualified to play for any club not even in the lowest division.
The same goes for Onana. He lost his confidence because everyone lost faith in him. Poor defense in the club also led to is poor performance. At least if Manchester United had a better defense most of is error will be covered up.