i did 140 miles to erie in one day a few summers ago. easily the most difficult ride i’ve ever done. half of that (difficulty) was because i was alone the whole time, and i tend to be a pretty gregarious person.
My longest single-day ride (defining a day as “from waking to sleeping”…I did get a shower and a change of clothes after the first 400K) was a 600K in Eastern PA, so a nominal 375 miles. That was over the span of 32 hours, though.
My longest ride in less than 24 hours is roughly in the 250-mile range (AKA “a 400K brevet”).
My longest day ws either follwing Swan’s Potato Garden Run and getting lsot (and misdirected) or on my back from a WV trip, going 70 miles that included crossing the Potomac on a railroad bridge and going slightly over two miles back and forth through roadless cornfields.
West Falls to Geneseo was 50 miles, which I did once when I was 19 (1977). The most recent longest ride was in March, McCandless to Library, then Downtown to Highland Park, for about 48 miles. Same bike.