Depends.
Sharing some things like this is perfectly normal. Itnot like it's a secret that you are in a relationship, and adults in relationships do have sex, it's nothing to be ashamed of.
There are some times when it's absolutely imperative that people should feel free to talk about it, eg if their partner is introducing things into the bedroom that they don't want, or forcing/pressuring them into sex that they don't want. People need the support of friends and family if they are accidentally in a relationship with an asshole.
I would agree that it's inappropriate to speak to anyone about performance/technique issues that cast their partner in a negative light, as long as the partner is doing their best and is considerate of their needs.
"I'm thinking of divorcing Ben and one of the reasons is that he doesn't care whether I enjoy sex, he hates foreplay and just uses me as a thing for his own pleasure" - fine to say, Ben has only himself to blame.
"Ben is doing his best but really need to get an anatomy diagram and work out which bit is the clit, he was there for ages and nothing happened for me" - cruel and inappropriate to share.
"Omg Ben took me to heaven and back last night, I am so lucky" - fine in moderation but not too much detail please.