Porch flooring: vinyl click & lock planks an option?

I'm not a flooring expert, so take this with a grain of salt...

So long as you're willing to accept the fact that you're using a product designed for indoor use in an outdoor application and that means:

• it's likely to fail earlier than you'd like
• it's likely to fail in less time than is claimed on the tin
• that any guarantee on the flooring probably won't be honored for being installed outside recommended parameters

I can't see a reason not to.

Some points to consider:

• It might be slippery when wet, you may want to choose something textured
• I've seen ads for "100% waterproof" flooring designed to resist spilled drinks, dogs peeing, etc. This is probably more expensive, but may be better suited for your more humid outdoor installation.

As far as your concern about tiles, remember that many in-ground swimming pools are tiled and have tiled/concreted decks and they survive in northern climes. Of course, they have the advantage of being directly on the ground and getting some heating from the ground itself, but the upper edges are well above the frost line.