It seems that Second Thought (and their second channel, First Thought) has been silently removed from Nebula, with no comment from them or anyone on Nebula’s side.
There’s some context in the comments of a couple of reddit threads about this, that have been deleted on the Nebula subreddit:
https://www.reddit.com/r/Nebula/comments/17be8bf/second_thoughts_channel_being_removed_from_nebula/
https://www.reddit.com/r/Nebula/comments/17bav9j/what_happened_to_firstsecond_thought/
The things I note are “Some Nebula creators” is not Nebula itself. And second, that he left before Nebula could remove him.
I find it hard to blame Nebula here, regardless of your stance on Israel.
I thought nebula was run by the creators essentially. At least that’s how it’s presented in the ads for it, so it does sound like this is nebula forcing creators to hide their opinions.