It's beginning.
The NFL team salary cap for 2021 is $182.5 million, down from last year's $198.2 million. The annual salary cap is based on the previous year's league revenue. Teams already have trouble re-signing their own players, and going after free agents when the salary cap increases each year.
Most key players already have their contracts for 2021 - but typically those contracts are not guaranteed and the teams can release them. With less money available, this is going to happen more than usual this offseason. We're already seeing it. I think most teams are at or close to the limit already, so there is going to be chaos regarding keeping and signing players.
In a perfect world, the players who caused this by turning off the fans would be the ones released, and then re-signed somewhere else for the minimum.
Next up, the NBA. They too have a team salary cap based on league revenue, and they too have lower revenue because their players went out of their way to alienate their fans. They're in an even worst situation than he NFL - they can't dump contracts, and their revenue will have fallen by a much larger percentage.