Next month the peony growers in your area will start their fall digging so you are safe to remove the foliage if you wish. While it might be any number of fungi it looks more like the leaves were damaged by hail. Since there are fungi that do have that look toss the leaves and stalks in the trash rather than composting.

Agree it appears to be a fungi. Hard to tell from the pic, but it looks like they may be planted a bit too deep.

If your peonies bloom, they're not planted too deep. Peonies often develop botrytis, which blackens the leaves and looks awful. But it never kills the plants. If you trim any peony with botrytis, sterilize your pruners before using on another peony.

That appearance would be totally normal for my peonies. In addition to spots, mine develop a grayish mildew also as the season progresses. I cut the ugly foliage off around Labor Day each year because that's as long as I can tolerate it. They grow & bloom wonderfully.

in MI.. especially in drought... the P can go dormant in late july/august ...

all you are seeing is the beginning of such .. and you need do nothing about it.. imo ...

the leaves are still processing sunshine and storing the energy in the roots for next season ... if you cut the leaves off too soon.. you can interfere with such ..

mom and dad had P in our yard when i was a kid.. and 50 years later.. i still have the plants ... and frankly.. they look like this every year.. and we NEVER treated for such... and it had no long term impact on them ...

it is really hard to kill a P ...

in fall.. if you remove the leaves.. maybe just leaving 3 or 4 inches of stem.. so you know where they are in spring ... then you will have removed anything that might be a problem next spring... but you dont need to even do that ...

if youve had a lot of rain this spring.. that might be why it has appeared a bit early this year ...

ken