Just wanted to place more emphasis on the information you provided. The current collective bargaining agreement is a 31-year-old modification of the original, that began in 1993, and has been re-agreed upon by owners and the NFLPA in 1998, 2002, 2006, 2011 and 2020.
Just like any agreement, labor language has been added to and subtracted from the CBA over the decades. However, the provisions for the league's salary cap and free agency have remained essentially the same.
As you stated, the CBA will not be changed until the owners and players union come to an agreement for a new CBA after the current one ends. That said, there is extremely little reason for anyone to believe the salary cap and free agency system will get tinkered with by either party at that time.
The last 'major' adjustment was done for incoming rookie salaries. Basically, the union deferred to amending the agreement because they--e.g. veterans--did not agree on the logic of players entering the league and making comparative or larger compensation before taking a single snap.
Under a hard cap structure, any restriction placed upon one position, say, veteran quarterbacks, would invariably be assigned to other positions as well in some form. The owners would love that. The players? Their agreement is exceedingly doubtful. Career longevity is typically short for most players. Players gun for pocketing the most money they can get before their time runs out.
Quarterback salaries may start leveling off after 2031. I wish I was from Missouri. The owners must show me they would stop whipping out their checkbooks for me to believe it.