This would be the year to spend the money, because 2020 and 2021 are both merged for FFP reasons, we could sort out all out problem positions as we were planning to, and then add Messi with most of next summers transfer budget.
Personally I think there could be litigation over the clause he has in his contract that lets him walk away for free. There's supposed to be a deadline but COVID has messed with the FIFA calendar.
Also the Webster ruling would be the nuclear option. If he ponies up his remaining salary of €71m, Messi can unilaterally end his contract. To be recompensed by his new club of course.