Do you know whether football related debts are just for transfer fees or whether it also covers wages owed to players to fulfil contracts as well?
Looking at the 30/6/21 accounts (appreciate a lot has probably changed since then to the 30/6/22 set), it appears that the club owes 27m for player registrations - 12m in less than a year so have been paid by now and 15m greater than 1 year (KG I presume). Can't think of anyone we have bought for any great money in the last year so that means we would owe around 15m as at now. For context, the club was owed 1.5m less than a year and 700k more than a year.
If that whack was to be paid before MSD in the event of an insolvency it would take out a large amount of their security, but as you say, there seems ample anyway - fixed assets are in the books at 77m so a 20m loan is in effect approx a third of the book value
If you do have factor in player contract payments ahead of loan, then this would change the landscape somewhat as the annual wage bill was 77m (although that would look to halve as this is the prem figure)
To answer your question about charge over holdings shares, given the fact that the owners reside 5000 miles away in a very restrictive country and there is a history of loans being given at low rates and not paid back i would also be surprised if something hasn't been put in place. Maybe not with any real intention of having to call it in but mainly to stop any silly bollox going on with respect to dividends/loans being paid to effectively take the £20m back out!