@gollum could you find this movie- Jak chutná smrt (1995)
It states that son watches his mother sex with a younger man at gunpoint.
www.imdb.com/title/tt0113452/?ref_=ttpg_ov_bk
The description you gave is incorrect based on this synopsis:
The criminal plot depicts the search for a young man who killed two traffic police officers in a short-term action. This crime brought the world to a standstill not only for the ambitious sports shooter and promising Olympian, but also for his parents. Robert's father, Karel Kainar, a former successful national team player, former Slovak politician and now a prosperous businessman, wanted his son to be even better than him - so he prepared the best conditions for him. After the fateful event, the loving mother tries to help Robert and inadvertently causes another tragedy. The lover of both men, model Daniela, also plays an important role in the family drama. The plot follows the police investigation and the actions of individual characters and reveals the motives of the young man's act in numerous flashbacks. In general, it is another "news" about increasing violence, resulting, among other things, from a certain lability of some young people who grow up in prosperity, but who pay the price for their parents' ambitions.
The son did not see his mother, but rather slept with his father’s mistress, Daniela (Ivana Christová)
While waiting for @gollum to upload the entire movie, here is the scene in question:
sendvid.com/ro0bl0my
celebsroulette.com/videos/18229/ivana-christov%C3%A1-in-jak-chutn%C3%A1-smrt-1995/
fr.eporner.com/video-Wy3G3dBq89J/ivana-christova-in-jak-chutna-smrt-1995/
pornone.com/fr/slovaque/ivana-christov-in-jak-chutn-smrt/280600441/?rr=161
There is almost no nudity, except for a close-up of Daniela’s breasts which, even with a slow motion, only lasts a few seconds.
