Not the PP, but I can think of a few situations that might change my reaction.
In most circumstances, I think that blocking someone is a really egregious thing to do, I'd figure out how to leave (other door, call someone, call 911, something else), and then we'd be on a long pause in our relationship.
However, I've also had elderly relatives who have shown really marked shifts in their behavior, including things that seemed hostile or paranoid. Those relatives pretty quickly wee showing other signs of dementia. So, if the person who did this as acting out of character, and as older, I'd have to at least wonder if this was a sign that they needed my help and support, rather than my anger and distance. For either my mom, or my in laws, that's probably where my mind would go, since this would be way out of character.
I could also imagine a circumstance where blocking someone would be legitimate due to safety reason. Am I drunk and walking out with my kid in my arms intending to drive? Is there a safety issue outside that I don't know about, like a fire?
Other than those three, unless it was super brief (e.g. my FIL stepped between me and the room where my kids were on mother's day and said "shhh they're setting up a surprise, give them a minute", or I've stepped in front of my mom when she goes to the kitchen and said "let me do the dishes, you've done so much!") of course in both of those situations, if I or my mom had continued to move then we'd be allowed to go, but unless it's something like that then I can't really imagine it not raising red flags.
OP, we need more information to be able to give good advice. An 18-yr old who wants to elope with her loser no-job 35-year old boyfriend? Yeah, as a parent, I might try to stop that. Controlling parents who just don’t like decisions their independent adult kids are doing? No way. Any abuse by the parents? No way.
NP. If the person were drunk, having some kind of dangerous mental health issue, or you knew they were leaving to do something reckless/dangerous... those are valid reasons for preventing someone from leaving.