There is a way to report ppl in this mode?

Not to my knowledge, but there is an in-game mute function now. Not as satisfying, but just as effective.

Here's a question: How? How are they specifically harassing YOU?

(In over 240 TFT games, I've seen maybe one toxic player!)

Correction: Account 1: 259 games (Gold I almost Plat IV) Account 2: 71 games (Plat IV) Account 3: 59 games (Diamond III)

Only once have I seen someone reportable toxic.

I'd send a ticket if you are having an issue in the mode. Depends what you define as harassment though. Some folks are crying harassment because players won't get out of the circle once they pick their champ/item from carousel. I've played a lot of this mode and thankfully haven't had issues (other than petty stuff like folks messing around during carousel, which hasn't been an issue yet).

There's literally an option in the post-game screen. Exactly where it's been for the past god knows how many years.