With residential fieldtrips we tend to emphasise the community/social side of the trip: that students can get to know their peers better and it is viewed as a bonding exercise.
However, for students with social anxiety this can be a negative. What I’ve done in the past is to make the social activities optional. For example, we’ve not made the students do a quiz, or whatever we’ve put on for students to do. If they don’t attend, then there is no come-back to it. If they rather stay in their room or do something on their own, then that is perfectly alright. We have found that some of our international students do not want to do the social activities and I do not feel I should be making them do something they don’t want to do. Similarly, we had a student with severe anxiety who left in the evenings to stay with their parents (who luckily were close to the field location). It wasn’t an issue. I feel we need to normalise this idea that students should not have to do all the social activities we put on for them and make it very clear that there is absolutely no pressure, and it is not really an issue.