This question came up in the Online 10-day Retreat Nov 3, 2020, guided by Delson Armstrong. Day 5 was part of a daily 30-minute discussion on the suttas, the Dhamma talk and reflections.
Slightly edited to improve readability
Oh yeah, I would say there is definitely something to be said about meditating in numbers, if you’re meditating in a group.
I’ve had situations where even not necessarily meditating in a group physically, where you’re with people but meditating on an online group. Where just people’s meditation together, on that online group, had quite an effect on people there.
There is something to be said about meditating together, It definitely starts to strengthen the quality of the Metta, for example, or whatever the Brahma Vihara is. It is quite useful to be able to meditate in large numbers.