There are spell construction mechanisms, but they end up getting very crunchy fast.

What a number of games do, to various extents, is to design the mechanics around the outcome of an action, not on the method of the action. Examples of this include Genesys, Avatar Legends, and Wild Ones.

In Wild Ones and Genesys, you still roll a magic skill, but the difficulty and cost of the roll depends on what you're trying to do. Typically, it should cost more than it would to do the action through mundane means, so that you can't just use your magic skill for everything all the time. So, you want to use magic to float up a cliff - you take the target difficulty for climbing up the cliff, add a bit, add a stress/fatigue cost, and that's your spell. You want to persuade someone magically, it's riskier than just talking to them (outcomes might be more dramatic, difficulty TN or difficulty dice might be tougher), and costs some resource, but is doable.

The other tactic, as used by e.g. Avatar Legends, is to just be completely agnostic about the method. If you "rely on your skills and training" to achieve a goal, you make the exact same roll, whether your training is in earthbending or swordfighting. You just get to describe if you scale the cliffs with athletic leaps or magic earth powers.