I really cannot understand why it is the manager fault if the team is not playing well.
Personally, I do not like Solskjaer at all and indeed he must leave Man Utd but the team had the same results when Mourinho was on the team for example. It is not a manager's fail but a team fail. The whole team needs to be reconstructed from the beginning.
It's true that the current Man Utd team (including ole) has failed to achieve good results in recent times. But in cases like this, The manager takes a much bigger blame because part of his job is ensuring that the team delivers solid performances. So if they're not performing up to par, it means he's not doing his job correctly. This man utd team hasn't changed much since he took over (tactics, playing style), couple with bad line ups/subs doing games.
Since last season Man Utd fans have called for Ole to be sacked so it's only a matter of time now. Mourinho got sacked after they were humiliated by Liverpool. After their defeat to Tottenham, I'm sure they're considering possible replacements for him if there's not much improvement in the team's performances going forward.
Compared to players, managers have bigger roles to play. For instance, when we signed Jürgen Klopp in 2015, he changed things around and Liverpool started competing for top competitions and winning them.