All the posts I found around this were a bit outdated. Is there a way to see how many people are subscribed to a post/thread?
There is no OOB way to view these.
In V1, there is no API to see how many people are subscribed to a particular post/thread, you can only view these users at Board Level:
In V2, you can use the following query:
SELECT * FROM subscriptions WHERE target.type = 'message' AND target.id = '<message_ID>'