How would you approach a requirement that appears to need dozens of criteria-based sharing rules on one object?

My first assumption is that the requirement has not been normalised, because dozens of distinct criteria on one object is almost always many expressions of a smaller number of underlying categories.

I would work backwards from the audiences. If ninety conditions map onto six or seven distinct populations, then the fix is a derived classification field — a formula or a field maintained by automation — that resolves each record to one of those values, with one sharing rule per value granting to a public group.

That collapses the rule count, keeps the model comprehensible to whoever maintains it next, and stays inside the documented per-object limits on criteria-based rules.

If the logic genuinely cannot be derived from data on the record — for example it depends on a related record's state or an external system — then Apex managed sharing is the legitimate answer. But I would present that as a decision with ongoing cost: recalculation classes, test coverage, and a permanent maintenance obligation.