Scenes occur during gameplay -- they don't require unlocking. To view them later in the gallery you have to unlock them. The placeholder unlock system has disks containing the scenes drop randomly from enemies. You can also purchase them from a vendor in the Void Slums.
Viewing post in Pure Onyx - Alpha Release June 2023 comments
To view them in the gallery you'd need to unlock them. You can see them as many times as you like during gameplay, they just need to occur organically. Also, not all scenes are available in gameplay yet. Regarding gameplay, not sure, maybe someone has posted a video ^-^. Most sites showing H game videos are super sketchy though >_<