1st Para - Chelsea seem to be gaming the system successfully so as to manage their finances (also made some canny transfer sales), but Barca are in an even worse financial position than MU - absolutely dire, in fact. Basically they've sold off, mortgaged or pawned just about everything they can in the effort to keep up with Real, PSG and the English clubs. (It's why they were desperate to get the European Super League going, may they and it rot in hell).
As for the Glazers or Ratcliffe putting in money, they can do so for infrastructure, womens team and Academy etc, but spending on transfers, wages and agents' fees are subject to a cap, which they're already likely pushing. While under pressure from UEFA, the PL is bringing in new rules which restrict this spending to a percentage of revenue generated. Now fair enough, MU still generate huge revenues, but much of this is presumably taken up by debt servicing, which will probably continue to rise, at least without European football, plus low PL prize money for finishing 15th etc.