The breaking point for verisimilitude is for every person different.
Like people complained about GOT TV Characters staying fat wild being month in the wild with barley any food.
That can be a deal breaker, because we expect fat people to loose weight when they don't have food.
It wasn't for a deal breaker for me, but I can understand when it puts people out of the fantasy.
Like for example what it did for me where the first two JJ Abrams Star Trek Movies, where for cinematic effect the flight times were reduced to seconds between different solar systems and were a cadets was put as a captain and stuff. It was all stuff that Star Trek did before but it was so over the top, that it just ruined the movies for me.
Or the super nova that destroys several star systems. I was like - what is that stupidity! Super novas don't behave that way!
While later I read up on that and I was wrong. Supernovae can be so big that they destroy several Star systems ...
So you see, verisimilitude is quite subjective and can also be based on wrong notions of what people think is realistic. I can tell you what I think would break verisimilitude for a lot of people:
If humans wouldn't be humans anymore in an TTRPG.