The AK-74 cannot be operated with the PBS-4 for a number of reasons.

1) The PBS-4 was supplied exclusively with the AKS-74UB.
2) There was a PBS-2 for the AK-74, but it never went into production.
A serial silencer for the AK-74 called the TGP-A appeared in the early 2000s.
3) The PBS-4 device simply won't fit the AK-74 mount.

In 1989, special forces had only 2 main options
AKMSN with a PBS-1 silencer and subsonic cartridges
AKS-74UB with a PBS-4
(In this case, we are of course not taking into account other special products such as the VSS special sniper rifle, which entered service in 1987, and the AS special assault rifle. As well as a number of pistols such as the PB APB and PSS)
We are only talking about the weapons that are already in the game.
I already wrote about this in detail in the Discord channel, but it seems it was missed, so I’m writing it here in a more concise form.😄

"Another special variant was the silent AKS-74UB assault rifle, equipped with a PBS-4 suppressor and adapted for firing 7U1 cartridges with subsonic bullet velocity.

The silent AKS-74UB assault rifle (GRAU index 6P27) featured a modified bolt with a plunger ejector and a modified cocking handle, as firing subsonic 7U1 cartridges required manual reloading due to the weak propellant powder charge. The assault rifle was equipped with a special iron sight with two rear sights for firing standard and subsonic cartridges. Standard 7N6 cartridges could be fired in standard mode (single shots and bursts), with automatic reloading, without removing the suppressor. The PBS-4 silencer (silencer) for the AKS-74U had a traditional design with a removable block of metal separators that slowed the propellant gases escaping the barrel. The front of the silencer featured a small spoon-shaped protrusion that served as a muzzle rise compensator when firing 7N6 rounds at supersonic speeds.

The AKS-74UB assault rifle, adopted in the early 1980s, served as the basis for the "Kanareyka" silent assault rifle-grenade launcher system, which featured a 30mm GSN-19M silent underbarrel grenade launcher. This system was a development of the "Tishina" silent grenade launcher. However, the AKS-74UB assault rifle proved unsuccessful due to the low effectiveness of 5.45mm cartridges with a subsonic bullet (bullet weight 5.1 grams at a muzzle velocity of less than 300 m/s), and had very limited use."

It is for this reason that special forces and reconnaissance units continued to use the AKMSN as their primary option until the introduction of the TGP-A silencer for the AK-74 assault rifle in the mid-2000s.
Below I'm attaching a photo of the AKS-74UB with a modified sighting bar adapted for firing subsonic cartridges, as well as a photo of the PBS-2, which was not used anywhere except during initial testing.😄

Of course, I should mention that the sighting bar for the AKS-74UB assault rifle, designed for firing subsonic and standard rounds, has two modes, as the subsonic bullet's trajectory differs...

BUT THAT'S A WHOLE DIFFERENT STORY😂

Also, if the developers are curious about what they're doing in the game, I'm attaching a video with a detailed breakdown of the product's creation.

The video is in Russian, but the English subtitles work more or less adequately.
https://youtu.be/5lLZBVRqXd4