For my experience:
Facebook - mainly promotion is done through groups if you can find the right audience
Reddit - just like the above. I believe it much affective as I able to gain 200 views alone from it
TikTok - no idea. I might try to get into it as a lot of people mentioning about it
Instagram - unless you have a huge follower and have close connection with them (not just stranger), it won't help much. It like out of those 100 followers, only like 10 - 20 people might watch your videos
I've always thought instagram was the way to go. But seeing how TikTok is on fire right now that is probably the best way to help grow your channel. Though I'm not really a fan of it considering all the cringy videos posted on there. But oh well right?