Oh definitely. I assume that RAI this is the intention.

I've never liked arbitrary spell targeting restrictions. I say if you want to fire blindly around cover or into a fog cloud you should be able to. It doesn't come up very often and because it's easy for players to understand that they'll have a very high chance of missing and losing the spell slot.

The humble cone of cold:

Yeah I thought of that one as well. It’s one of those weird cases of imprecise wording.

By that logic you can see air because there's clouds in the sky.

Or just interpret it as line of sight.

• Detect magic.

As I have said in another comment, that is RAW not what would happen:

"You can’t even cast it on something behind the wall, because you cannot target something (or someone) with a spell if they are behind total cover. Total cover is created by being behind completely behind an obstacle (like a wall). This counts even if the obstacle is invisible."

Furthermore, because if you chose an invalid target for a spell, you’d still expend the spellslot but there would be no effect. So you actually spend a sixth level spell a lot to achieve nothing."

It’s very much not RAI I'd say and I would likely handle exactly like you described, but the RAW was so wonky that I wanted to make the meme when I found out about it.

Or a bag of flour to throw around to make the wall visible

Nope

Yes. See invisibility should work as well. Both are quite annoying to activate when in a fight though.

Edit: TIL that detect magic may not work, because the object has to be visible.

No. If we assume that you have to target the wall it would at the very least stop after destroying the wall.

But by RAW, you can’t even cast it on something behind the wall, because you cannot target something (or someone) with a spell if they are behind total cover. Total cover is created by being completely behind an obstacle (like a wall). This counts even if the obstacle is invisible.

Furthermore, if you chose an invalid target for a spell, you still expend the spellslot but there will be no effect. So you'd actually spend a sixth level spell a lot to achieve nothing.

I would not recommend doing it this way, but that’s what the rules say.