How do I stop "Posted a Story" from popping up while watching TikTok Videos?

I have one friend, that posts a LOT of stories on his TikTok. Every time he does, while I'm browsing TikTok, I get a pop-up notification within TikTok that says "<username> has posted a new story". It's getting annoying and I can't stop it.

It *only* happens with him and no other friends. I thought I disabled all notifications like this in my profile and for him directly, but it's still happening... and from what I see in TikTok settings and such, this is true.

Please note, this is not a phone notification but a notification within TikTok in itself.