I've seen toxic positivity with my own eyes, when I joined MLM. The usual small talk goes like this:
Guy: " Hi, how are you doing?"
Me: " Pretty good, nothing much.."
Guy: " Hold on! That's a completely wrong attitude! What you're supposed to say is 'I feel amazing'"
Me: "okay... I feel amazing today?..."
Guy: " that's much better! You can't let negative thoughts ruin your day! Always think the positive side!"

It became ridiculous, when his upper level contact fell into depression and this guy (along with the other yes men) ranted how weak his contact was for letting negativity influence his thoughts and not trying to get back into positivity.

The last straw was when one of the guys lost a friend in a car accident. He was avoiding the topic around the others. I went for him to let him know I was sorry for his loss. Later the yes men brought that up to me that I shouldn't talk about this car accident, because it affects negatively on the peers and that's something the guy needs to tackle himself.

The irony is that the material where they learned all about the positivity attitude doesn't even encourage suppressing negative thoughts. It literally says right in the book, that sometimes there's issues in life and it's completely fine to have bad days and grieving, but also face your emotions and seek for recovery. The yes men completely ignored this part.