Expedition: general discussions.

In principle, this sounds interesting, but the downside is that the GM will often have to determine the mechanics of such things on the fly. For example, a column and a ceiling should have a certain number of hit points, and the mage needs to inflict enough damage with his earth magic for his action to work. The number of hit points will have to be invented on the spot. I personally like this, but won't there be complaints later in the thread that some ceiling is too strong and couldn't be collapsed in one turn?

I don't quite understand the point of this fuss with "hit points" when the emphasis is on creativity and adapting to the situation. The player asks if something is possible – the GM immediately answers whether it is possible (although he may conceal it, of course), deciding for himself how many uses are needed (if the effect will even work). Hit points are a completely foreign concept here. They would make sense, say, if the player wanted to knock a chandelier onto an opponent with an arrow (and then the GM would have to figure out what and how, if he hasn't devised a system for such cases), but not here.

Automatic success of any "creative" action is also not an option.

But no one is talking about automatic success. Besides, knowing the players' plans, they can sometimes make things more difficult for themselves with such creativity.

So, in the end, it's not entirely clear. It's up to you. I would try to anticipate such possibilities in advance
(for example, in the description of the earth beam, I would write that it can destroy objects with a mass of no more than X, etc.)

There are situations when players come up with a creative idea for using an ordinary spell that the GM hasn't really thought about. In other words, it was intended by the GM for one purpose, while the players decided to use it for another, and no system was devised for this. That is, in such situations, everything will be decided by the good old GM's discretion.