What the salary cap will be in future years is usually a bit mysterious. Yes, we all know that the league is getting more revenue with new TV and partnership deals. However, the way things have generally worked is not quite the same as the way the media reports it.
The salary cap will go up each year . . . but it is predicated on going up AFTER the league starts getting more money. They space out the increases across the life of the labor deal with the players. In recent years (2020 excluded), the league has typically bumped up the salary cap $10M per team per year. So in a 5 year labor deal, compared to where things were at the time the last CBA ended, the increase in contribution from the league to the teams and players in terms of extra salary cap dollar would look like this: $320M + $640M+ $960M+ $1.28B + $1.6B = $4.8B total additional money added to the cap over 5 years.
When the media reports that the collected salary cap fund is going to go up by $5B, that is true but it is scaled up over time and not all at once. I can't tell if the media doesn't get that or if teams think there will be a new paradigm and the salary cap will take a huge jump all at once. So far, the league hasn't done that.
This year's salary cap is pegged at $208.2M . . . which if things stay the same, next year that would project to $218.2M. Miami has roughly $16M in existing cap space left as currently constituted for 2022. They could extend players, redo contracts, sign new players, etc. with a long way to go until opening day. If they don't spend to the cap, any leftover money will roll into next year.
Anyway, as of now, Miami has $208M already allocated for the 2023 season. That doesn't include any dead money they might incur, any incentives that they will have to pay out on current contracts, any dummy years on contracts that they will have to take cap hits on, etc. If the cap actually turns out to be $218M next year, the Dolphins are already at $208M of that . . . but they only have 34 players signed (51 players count against the cap).
Long story long, your point about cap management is very valid. Tua only counts $9.6M against the cap next year. After that, they will either have to pay him more to keep him or bring in someone else. Being already up against the cap without having a long-term solution at QB could require a lot of cap gymnastics moving forward.
ouglieDoWrong: 
. Talent leaving, meh coming in. Watching what is going on down there is fun!
