The modern game changed, not the systems. The bones are still 3/4, you just rarely see that exact alignment because passing has become so prevalent in the NFL.
You mostly see now what would have passed for nickel defenses 10-20 years ago. Teams no longer roster four stud DT’s who can also play nose tackle (Washington, Seymour, Warren, Wilfork) instead teams only roster 1-2 of these guys and maybe keep one big run stuffer on the practice squad.
A guy like Mike Wright who was a situational interior pass rusher for the Pats decades ago is now more common as an every down player. Decades ago Milton Williams would only have played DE in a 4/3 defense, now he’s a higher snap guy because DLinemen have to play more snaps, they have to be able to stuff the run and rush the passer and stay on the field.
The system is still 3/4, but it looks like a four man front because of alignments.
Something like this, starters in bold with a lot of rotating based on down and distance:
DT – Christian Barmore, Khyiris Tonga, Joshua Farmer, Jahvaree Ritzie,
DE – Milton Williams, Keion White,
SLB – Harold Landry, Anfernee Jennings, K'Lavon Chaisson, Bradyn Swinson, Elijah Ponder,
MLB – Robert Spillane, Jack Gibbens,
WLB – Christian Elliss,
SS – Kyle Dugger, Jabrill Peppers, Marte Mapu, Marcus Epps, Brenden Schooler,
FS – Craig Woodson,
BIG CB – Christian Gonzalez, Carlton Davis, Miles Battle,
SLOT CB – Marcus Jones, Marcellas Dial,