It is a four year deal.
They could have had him this year for $23 million.
Franchise him next year for about ~40
Franchise him the following year for less than 50 million
If they then signed him for a $100 million dollar one year deal. That would still be considerable less expensive for the dolphins than this four year deal.
This is wrong. The contract is a 4-year *extension* with $212 million in *new* money, so you don't get to count the "could have had him this year for $23 million".
Let's assume you could actually get him play this year on his old deal with no ill effect and that you could franchise him twice. That's $23 million for '24, $42 million for '25 (the projected franchise tag value), and $50.4 million for '26 (120% of previous years' salary). That's just over $115 for 3 years and you need to sign him for another two. There's a lot of money left to do it, but not anything like "over $100 million".
Obviously, you wouldn't get the short term cap savings (he will count $9.5 million against the cap this year, but similar amounts to the franchise tag alternate-reality for the next two).
There's also an out after 3 years according to OTC, where a pre-June 2027 cut would save the team $36 million in salary cap with only $17 million in dead money. In reality, I don't think that's the case, though, with certain amounts of Tua's salary that become guaranteed at later dates. The reporting on the details of the contract is a bit vague when it comes to details like this, but the hit would likely be $3-$20 million higher.