Peony cages is the only solution for flopping of old-fashion peonies. Generally the biggest ones are 18 - 24 inches in diameter. If your clumps are bigger I suggest ordering someone to make new or fixing your old ones. Klehm's Song Sparrow are selling one, but they are not cheap. Someone mentioned that they are great - I did not use them, second hand knowledge.

Another option - Allan Rogers advises a single pass
of heavy-duty garden twine around the plant, about a foot from the top,
after the buds are enlarging in size. Alternatively two lines, one
twelve inches from the top and the other twelve inches below that.

Large tomato cages cut in half work well. You'll want to use bolt cutters to cut it, though--takes forever with a saw. Azomite is supposed to help make stems stronger but if yours are the old fashioned thin stemmed kind with huge blooms I don't think anything other than cages will work. Someone posted a pic on the other peony forum of a Festiva Maxima that was enormous and beautifully mound shaped. Said the owner put a cage over the middle part and deliberately let the outside droop--looked amazing.

https://www.treepeony.com/pages/visit

They sell umbrellas for to protect peony blooms.