I can't remember,
@lookingforsunshine, have you done Marathon Weekend before? If so, you'll have a pretty good idea of whether you'd have FOMO from not doing the four-race challenge. If not, it may come down to your personality and how you feel when surrounded by an atmosphere focused on something other than what you're doing.
A number of folks have reported not having FOMO while doing fewer races or Goofy. I'm the opposite. I ran the 10k, 1/2 and full my first Marathon Weekend (no challenge registrations at all). It was my first RunDisney event and I was floored by how focused everything seemed to be on the four-race challenge. So much so that I didn't feel like I was experiencing everything the weekend had to offer. The next two MWs, I ran the four-race challenges (even though 1 was 2017) and loved being a part of the central atmosphere. In 2019, I thought "been there, done that, have LOTS of shirts" and decided to run Goofy to save on $$$ and vacation days. I absolutely hated that weekend and felt like I wasn't getting the most out of my experience. Now it's just the four-race challenge for me (registration permitting) every year.
YMMV, of course, but I just wanted to throw my experience out there, as the FOMO can be very real.