Yeah, it's a hardlimit of 32bit applications.
IE unless you get lucky with tinkering around with what mods you have on and your world size, your gonna need the 64bit version TMODLoader to even run Calamity at this point.
I really think this needs to be added to the front page under an FAQ, people who can't get calamity to work because of this are going to keep repeating the same issues over and over again and filling up this thread with the same messages because they can't be bothered to read if there's a fix in previous messages "Hint, Broken Essences from Fargo's mod because of Throrium, hint" (oh on that note, an FAQ about "not posting discord drama in this thread" would be appreciated too)
This honestly is not good, not only does Calamity require a unreasonable amount of RAM, but if goes 64bit only, it means non-64bit systems will be locked out of it, including non-windows systems too.
That's going to kill this mod's popularity.
But there isn't an easy fix in the slighest, making the music separate would help, but that would degrade the experience as a whole if you couldn't use it.
Calamity is in a similar boat right now as Dawn of War Soulstorm's Ultimate Apocalypse Mod: It's gotten super big and super popular, but super heavy too.