I think there are three broadly principled and internally consistent epistemological stances: Radical skepticism, solipsism, and realism. Radical skepticism is principled because it simply demands extremely high standards before it will assent to any proposition; solipsism is principled because it combines skepticism with the Cartesian insight that I can be certain of my own experiences; and realism is principled because it tries to argue to the best explanation for phenomena in general, appealing to unexperienced posits that could plausibly generate the data at hand.

I do not tend to think so highly of idealistic and phenomenalistic views that fall somewhere in between solipsism and realism; these I think are not as pristine and principled as the above three views, and their uneven application of skepticism (e.g., doubting that mind-independent cucumbers exist but refusing to doubt that Platonic numbers or Other Minds exist) weakens their case considerably.

This question is meaningless in the framework I have described (Experience + models = reality).

If commitment to your view renders meaningless any discussion of whether your view is correct, then that counts against your view. We need to evaluate the truth of "Experience + models = reality" itself, if you think the statement in question is true. (And if it isn't true, then what is it?)

If you provide an argument why this framework is not suitable, i.e., it fails to be useful in a certain situation, feel free to give an example.

Your language just sounds like an impoverished version of my language. I can talk about models of cucumbers, and experiences of cucumbers; but I can also speak of cucumbers themselves, which are the spatiotemporally extended referent of 'cucumber,' the object modeled by cucumber models, and the object represented by my experiential cucumbers. Experiences occur in brains; models are in brains, or in an abstract Platonic realm; but cucumbers are not, as a rule, in brains. They're in gardens, refrigerators, grocery stores, etc.; and gardens and refrigerators and grocery stores are certainly not in brains either, since they are too big to fit in a brain.

Another way to motivate my concern: It is possible that we're all mistaken about the existence of cucumbers; perhaps we've all been brainwashed to think they exist, for instance. But to say that we're mistaken about the existence of cucumbers is not, in itself, to say that we're mistaken about the existence of any particular experience or model; rather, it's to say that we're mistaken about the existence of a certain physical object, a thing in the world outside our skulls. Your view either does not allow us to be mistaken about cucumbers, or gives a completely implausible analysis of what 'being mistaken about cucumbers' means in ordinary language.