Here's a post with pictures from a wedding in Kfar Chabad with the 100+ people rule enforced.
https://col.org.il/news/123603I honestly don't see how the rule makes much of a difference. There's close contact, holding hands etc. Unless everyone has 100% awareness of hand washing and sanitizing OFTEN (probably in such a setting should be greater than 30 times per hour) this can easily contribute to the spread.
I was at my BIL's Chabad House Purim party this week. There too I saw 0 awareness. Buffet out there for everyone to help themselves, etc etc.
Maybe rather than limit gathering size there should be mandatory hand sanitizing stands every 10-15 feet in gatherings (and shuls).