UPDATE:
There are two ways to capture Midi Out from Logic’s Midi FX:
- Set up an External Instrument to capture:
 https://youtu.be/nSBdNPdMtkk
 https://ask.audio/articles/capturing-the-arpeggiator-output-in-logic-pro-x
- Install the free MIDI FX FREEZE from AUDIOCR
 http://www.audiocr.com
 (currently down for some reason, there’s a direct working link to the component at the bottom of this thread):
 https://www.logicprohelp.com/forum/viewtopic.php?f=1&t=140135