I'm sure I've even heard French people say "au jour d'aujourd'hui"

I'm pretty sure I've seen that one in a list, by a French person, of things they wish other people wouldn't say!

Yes, we had an epidemic of that about 10 years ago. It was everywhere. Thankfully it's mostly gone now and we're back to "aujourd'hui".

Also French: je ne sais (I don’t know) → je ne sais pas (I don’t know a step)

And recently even dropping the negation itself while keeping the meaning: “je sais pas”

I never thought about that. Interesting. This negation related cycle is apparently called Jespersen’s cycle and happens in many languages. The English equivalent

I say not -> I “do” not say -> I don’t say. -> ?

https://en.wikipedia.org/wiki/Jespersen%27s_cycle

Lived experience