This is the answer the OP is looking for.Damnation Audio MBD or earlier versions MBD-1 and MBD-2 have a Low passed Clean blend that should do the trick.
They also make a Dirt Fixer Pedal that you can use with any OD/Distortion/Fuzz etc to accomplish this as well.
Broughton Filter FX Loop is also a great way to achieve this with any OD or Dirt pedal you may otherwise like.
I'm sure there are a few other all in one pedal solutions, but the feature you are looking for is a "Low Passed Clean Blend" in case that helps!
Only thing I'd add is the Damnation Audio "Bloop" (Low-passed Loop Blender), which has now been reiterated the Dirt Fixer, is also a viable option (if you can find one secondhand). The Bloop is simpler and smaller; the Dirt Fixer offers more tone-shaping possibilities and features the contoured blend that's been mentioned in this thread already, but is also housed in a bigger enclosure.
Some pedals, the CMC Audio Proto Type, offer a bake-in low-passed clean blend: the amount of dry signal is fixed, but it is low-passed. I prefer the MBD because I like to determine the amount of dry myself, but if you, OP, don't need to adjust that and simply want it to be low-passed, then this could also work. This might be how the Broughton Scorpion works as well. (I'm unclear on this.) Some folks have pointed to the Scorpion's Depth pot as a way to control how much of the frequency spectrum is distorted--and it does work that way--but moving a HPF on the wet signal isn't quite the same thing as low-passing the dry signal. I'm sure Josh built some dry signal into the Scorpion's circuit, but just what that signal path actually is is not denoted in the Scorpion's description. Regardless, the MBD offers pots for both Depth and a low-passed/contoured clean blend so it seems the best fit for what you are seeking.
In case it helps contextualize my answer, I used to use an MBD-2 and also a Bloop (for other dirt). Now I have an MBD and my other dirt is in the loop of a Broughton FFXL.
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