The OK symbol is completely ok. There's nothing wrong with it. There's a certain sect of internet cretins who use it to dogwhistle to each other.
When someone uses the OK symbol, it literally means nothing. If that person also belongs to or is adjacent to that certain sect.. then you can start to ask questions but still mainly assume innocent intent.
If that person is using the OK symbol while wearing a MAGA hat, posting pictures with Pepe the frog doing the OK symbol, etc.. You can see clearly the throughline here and it's not illogical or wrong to see what that person is clearly trying to do and call them out on it.
I'm not 'decoding secret symbols', and if a hispanic person truly was fired for just doing an "OK" sign and nothing else, then no one who is serious on the left should support that as that is beyond absurd. For some reason, my bet is that there was a bit more going on than that though, but I could be wrong!