How to manage very weak students presenting problem solutions?
There are at least two+ different issues: (1a) your suffering (1b) suffering of the other students, (2) the obliviousness or incompetence or low-energy of the individual student. The easiest argument that there's something needing repair is that the other students shouldn't have to suffer, in any case.

My anecdotal evidence indicates that whether it's obliviousness or incompetence or some sort of lethargy, any one of these can be an essentially fatal obstacle, and is not within anyone else's power to change in the short term. Maybe long-term. Giving easier problems will not be understood as such, and can have the effect of passively "confirming" the inadequate strategies of that individual.

So: time limits on presentations, at least. Perhaps "failure limitations", too, meaning that a certain smaller window is allowed to persuade the audience that things are going in the right direction. This criterion gives a device to get failing performances off the stage and not waste other peoples' time.

Similarly, in my experience, it is possible to spend unlimited amounts of time on some students "with problems", thinking to "lift them out of failure", but have essentially no impact on them. Don't do it. Allocate the reasonable amount of time, and then stop. This is absolutely not an argument against spending time and energy on students (a.k.a. "teaching"), but is an argument against pretending that one has infinite personal resources, and against pretending that bad allocation doesn't harm other parts of the enterprise.

Possibly time to mention the Dunning-Krueger syndrome again, too? That is, that sometimes the most problemmatic scenarios are those in which someone lacks the meta-cognition to understand that they "even have problems". If someone has already passed/failed that filter, the chances are slim that you can call on their meta-cognitive faculties to help them... Sadly.

So, you cannot deny weak students resources, but don't misallocate so as to harm others. And the cost to you yourself should be limited. One does not have unlimited responsibility (in time or energy) to students. Definite responsibility, yes, but definitely limited.