This probably means the Leafs can't offer Matthews a $20mm p.a. or even a $15mm p.a. contract.
The cap number isn't changing because of this (as the TV contract is fixed for the next 3 seasons), so it has no impact on the max he can get.
$20m was never a possibility as the cap was never going to be high enough to grant him that.
The salary cap for next year is projected at 83.5 million. For the 2024/2025 it is projected at 87.5 million.
Auston is permitted to sign for 20% of the cap under the CBA.
If they extend him this summer (after July 1) it looks like they can pay him a max of $16.7 million.
If they sign him next summer its probably closer to $17.5 million.
Of course the Leafs would be idiotic to give him the full 20% of the cap, but the organization has been bending over for him since he got here. The 5 year contract (instead of 8) was one of the worst negotiations I have seen,