Spoilers follow:
these past few days I went and read the raws up to date with MTL and from what I could understand:
The only video that we see Sasha showing MC is one of himself and Sasha having sex, which gets him worried that Sasha could get blackmailed by having that kind of recording and it goes into a bit of a fantasy that in his head looks similar to the Sasha doujins. Also he is kind of surprised because that video is actually the first time he sees uncensored porn, the chapter ends with Sasha saying and I have videos "of/with other people" and then showing the MC pretty much overheated with that, but it is never explicitly shown that the other videos are of Sasha fucking someone else. Their first time is off-screened too btw.
Some chapter later a senpai appears that seems to have a past relationship with Sasha, he confesses to her and she rejects him saying she is more interested in MC and also that the senpai was too "possessive" before so she can't be with him, again it dances around the issue of them having sex without ever confirming anything, a bit later this senpai starts getting closer to the MC, Sasha gets jealous of being left out and it's not clear who proposes a 'three way' and a chapter ends, just to then show them playing at the arcade together and seemingly simply having a three persons 'play date', the only moment of sexual nature is one panel showing this senpai tied up and with a gagball in a corner while MC and Sasha read manga in what seems to be the school, really couldn't make up the context of how they got there.
My take is that yeah, this Sasha is not exactly a saint but also doesn't seem to be up to the same things as the doujinshi version, unclear with who or how many others she has been with or if the MC was her first, or maybe the senpai if that gets confirmed. It could be the limitations of the MTL with a context-heavy language like Japanese but so far it seems to be people have been blowing out of proportion the events.
Also I think that the author is likely also playing with reader's knowledge of the other Sasha versions, expecting us to wait the worst and then coming up with a twist, or leaving things so vague we can't help but imagine it went all the way.