SWIM has been wondering if a citric acid solution could be used to wash a nonpolar solvent, picking up DMT citrate but leaving behind plant fats, thereby avoiding lengthy defats. SWIM has seen this done with acetic acid, but there seems to be little information on citric acid in this context.

Is citric acid less effective for this, or is there another reason why acetic acid is more commonly used?

Sure, it works. I've done it.
Once when I was a combination of busy and lazy I brewed up some bark, based, extracted into xylene pulls, combined them, and from there extracted into a citric acid solution. I used excess citric acid so I wouldn't have to bother with titration. I then took the citric acid/DMT citrate solution, put it in a beaker, placed on a coffee maker hotplate until well after all xylene smell was cooked off. I cooled it and measured the volume, did the math, marked the bottle X ml = Y grams of bark and froze it. Any time I wanted to trip I fully melted the bottle, mixed it, took out whatever dose I wanted, and drank it shortly after drinking some harmalas. That bottle lasted me a year.

And then I made white crystalline DMT bifumarate so I can take it as a pill and not drink DMT mixed with citric acid

You can also go from DMT citrate to freebase DMT by a variety of methods.
Be warned, like many DMT salts the citrate reduces down to goo instead of crystals.

That is super interesting thank you for sharing.