I think the point you have made numerous times about Fred, that he should be given time to adapt, before making a final assessment, is correct. The list of exceptional performers who had a difficult first season in a new country, is a long one. The change of manager, especially his decision to opt for continuity in midfield, selecting Matic, Herrera and Pogba, game after game, made life even more difficult for Fred.
Where I disagree with some of your previous posts is a factual point. Here are Fred's appearances last season:
https://www.transfermarkt.co.uk/fred/leistungsdaten/spieler/191614/plus/0?saison=2018 He made 13 starts in the PL, 6 in the CL and one in the FA Cup, as well as 4 sub appearances in the PL and one in the EFL Cup. Transfermarkt estimate he got 1593 mins in total last season.
Fred possesses some talent, as do all our first team squad. I can understand why we were interested in Fred, as his skill-set is different to that of our other midfielders, especially given Pogba had persuaded Mourinho to use him higher up the pitch. The fee seemed high at the time and has turned out to be ridiculous. His age, added to the salary he is being paid and the transfer fee, indicated a regular starter rather than a back-up player. Criticism of the transfer, the scouting, is justified.
If you ignore the fee, I think Fred is a reasonable 4th choice central midfielder for a two player central midfield. He performed well against PSG away and Barcelona home. In the PL there were times when he looked out of his depth but other games in which he did a decent job of getting on the ball and developing the play. Like most of United's current squad, he needs to tighten up a few elements of his game, and increase the number of good moments. My track-record at predicting which players will develop their game isn't great. I tend to believe younger players are more likely to improve but that may be too simplistic.
Being in the team for EL and domestic Cup competitions, rather than the PL side, isn't ideal but it is an opportunity to demonstrate that he has taken onboard the advice the coaching staff have given him and a chance to make a case for inclusion in the PL side later in the season, especially if Solskjaer considers moving to a 3 man central midfield. AZ Alkmaar was just one match and shouldn't define his United career. In his other 2 starts this season I thought he did ok.
Finally, the big unknown at this stage is how long Fred is prepared to be a back-up player at United, assuming McTominay and Pogba continue to be the first choice pair. I would imagine that come next summer, we will have other priorities than spending limited transfer funds on upgrading our 4th choice central midfielder. If Pogba leaves then a huge overhaul of our midfield would be financially viable but otherwise I suspect Matic will force a move one way or other and United will need to bring in a replacement, while we wait for Garner to develop.