There is no easy fix, should have bit the bullet when Ten Hag came in and do a complete rebuild, don't extend Bruno, don't sign Casemiro and Eriksen, go for young cheap talent and suffer for a season or two.
But you can't do that, because then the lucrative deals don't happen, so the team is in this ever-ongoing patchwork mode where each manager comes in, signs some players, then does okay, until the next season when they get more players, but still not enough to implement their style they want to play, form goes to shit then that manager gets sacked and we get a new manager and start all over again.
I think the only possible fix is that when Ratcliffe comes in, he comes with his own CEO/DoF to run things and there will be a comprehensive plan going forward, some short-term pain for long-term gain, whether Ten Hag will last that long, who knows, expect to see him at a team like Barcelona though and win the LaLiga and the CL though after he leaves us.