Is Wet & Forget Toxic or should I just use TSP for mold, moss &mildew?

Not toxic except to the mold, moss, and mildew. Toxic stuff of necessity carries very visible warnings. Look at the bottle and you will find no such warnings. TSP, on the other hand, is toxic to you and harmful to streams and lakes. Laundry detergent, by law, no longer uses phosphates because of this.

https://www.bobvila.com/articles/cleaning-with-tsp-trisodium-phosphate/

For a non toxic Mold, Mildew, and Moss remover- use plain white distilled vinegar. It kills more varieties than bleach and is also able to permeate more surfaces as well.

The active ingredient in Wet N Forget is not carcinogenic. It does have some toxicity, but its dilution minimalizes the danger. As with all chemicals it's best to apply it dressed in long sleeves and pants and wearing a face mask to avoid breathing in the mists. Wet N Forget errant spray won't kill your grass and other plants, but it may cause temporary browning. Pets should be kept off of sprayed areas for 5 hours. Once the spray has dried it is safe to touch. However, sidewalks and such can be rinsed off with a hose the next day so nothing lingers.

I think I'd much rather use Wet & Forget than TSP, which is really toxic.

This product instantly kills small frogs ! That was surely not my intent when I applied this product . Please beware how toxic this is to use around your house ! I returned the product to Lowe’s .