Traditional Medicare (TA) has NO total out-of-pocket (OOP) maximum costs. Not only for prescription drugs (initial co-pays, 'donut hole', then 5% above that) but also for skilled nursing (even IF one initially qualifies, no coverage over 100d/yr) and inpatient care (no coverage over 90d/yr after one has used their "lifetime reserve days", lifetime max 190 mental health inpatient days). Private Medigap insurance can cover some of those gaps, but not all.
According to an Urban League study published this month, over 4 million Medicare recipients had over $5,000 in OOP medical expenses. Some 800,000 has OOP expenses over $15,000, with some much, MUCH higher than that.
Medicare Advantage (MA) with its HMO-like structure offers some OOPmax protection, but those limits are now up over $7,500k/yr ($11,300 for in- & out-of-network care if MA plan allows). And that does not include expenses not approved by MA (deemed "not medical necessary", which commonly crop up).
https://www.urban.org/research/publication/adding-out-pocket-spending-limit-traditional-medicare
DW & I are transitioning to Medicare this year and our total costs (inc premiums, IRMAA (TM supplement & Part D), deductibles/co-pays) will likely be a bit lower than when we were on ACA (no subsidy) & COBRA ... IF we have no medical catastrophe. But the lack of an OOP max with TM (or a 'true' OOPmax with MA) is (to use the OP's words) is a big feature where Medicare 'falls short'.