While I was initially trying to get set up in NeoForge 1.21.1 for the very first time on test worlds, makng sure that everything's going smoothly and all, when looking in the logs that there's major error spamming with the compats for most of the mods such as curios and ancient reforging. That indicates that the compatibility code is possibly broken and needs to be fixed 'cause the error spam is bad for performance and could cause TPS lag (possibly not the perpetual TPS lag that I've experienced in the past on Forge 1.20.1 but still).

I'll mention issue #5 in this issue report since I'm seeing the same overlaping error in the curios compatibility code that Phoupraw saw and reported.

This addon was one of the reasons why I added in The Twilight Forest to my new 1.21.1 world, since it's been years since the last time I've really been in there and never paired it with Apotheosis before.
I have paired both curios and apotheosis before with apotheosis capable of letting Sophisticated Backpacks's backpacks getting affixes and gems as well and can go in the back slot in curios, but the apothic attributes only applies to when actually warn in the chestplate slot instead of the curios back slot. Which I don't exactly like that which is another reason why I wanted to get this mod is for that exact thing.

So for now until you resolve the compat issues that this mod currently has, I'll not be including this in my newly made Neoforge 1.21.1 world because I don't want the constant log spamming with the same errors over and over throughout the entire time I'm playing. Since my performance in modded mc is bad enough as it is already and what if these exceptions cause an exception which would cause the game to crash eventually? when I've crashed about five times already during my last session...

Latest Log: https://gist.github.com/Coraline774477/9778c47bf956b5d7b8864234d8848ea9

EDIT: The Ancient Reforging thing is an NullPointerException in rarity_override file in apothic_compats:apothic_compats while there's an IllegalArgumentException in affix_loot_entries file in apothic_compats:curios that's obviously associated with the entries in the rarity_overrifes file in apothic_compats:

back > back_plate
necklace > ornamented_necklace
ring > ornate_ring
charm > fancy_charm
curio > embellished_curio
feet > adorned_boots
body > body_chain
head > head_cover
hands > showy_gloves
belt > florid_belt
bracelet > flasy_bracelet

One more thing: in Phoupraw's issue report, they're missing some information, such as:

Exception while applying ExtraGemBonus apothic_compats:curios/apotheosis:

the_nether:
inferno
molten_breach
blood_lord

overworld:
earth
verdant_ruin
royalty

the_end:
mageslayer

twilight:
forest
queen

core:
solar
guardian
combatant
warlord
ballast
tyrannical
splendor
samurai
slipstream
lightning
lunar

Oh, and I don't have Ancient Reforging installed, since I never heard of it before nor would I want to add that mod to my world when my mod list is full enough as is.
Since I was thinking about adding Project MMO to spice things up but decided to go against that idea and to be honest, I don't know if it's for 1.21.1 Neoforge anyways, possibly but unsure though.

So, I looked into Apotheosis's changelogs and between versions 8.3.0 and the latest version (which is 8.3.6).
In 8.3.0, shadows may have broken your mod, rendering it currently and completely useless since it's not compatible with 8.3.0 and above.
Also, The Twilight Forest compat has been re-added into Apotheosis, so this mod no longer needs to add compat for The Twilight Forest.

I've found out that 0.1.7 is the update to work with apotheosis 8.3.0 but apotheosis is at 8.3.6 now and the log (and possibly the console obviosuly) are being spammed with what I've said above a week ago.
I looked into apotheosis's github changelogs and found nothing relating to my findings that could've explained why apotheosis's latest version is borking apothic compats. Also, you only listed the compat with 8.3.0 and nothing else which could possibly explain why 8.3.6 is breaking apothic compats.

Btw, Even though I had mentioned about TTF compatibility and that Apotheosis had re-added TTF compat but apothic compats description still says that it adds TTF compat even though apotheosis already has compat with The Twilight Forest since 8.1.0.

One more thing, I'm thinking about adding Ancient Reforging but I think that it's gonna be the same situation as with Apothic Compats. I'd rather wait for you to fix possibly both mods to work with 8.3.1 and above so that the spamming would stop

i've updated the mod to many of the newest versions of mods, so let me know if anything is resolved, the log spamming i'm looking into because im not sure whats going on there. ive worked with shadows personally to make sure this works properly, and there is alot of log spamming that can just be ignored. but i understand that concern

regarding the ttf compat, there are some things that i add personally that arent in the compat given with apotheosis, therefore i have listed that i add more compat.

so unfortunately for the time being, the log spam is something out of my control. i spoke with shadows about this issue specifically and he said that it is an underlying issue with placebo that needs to be fixed at some point, so i cannot do anything about these log spams on my end of things

the spam problem should be fixed in the newest placebo & next apotheosis update

Thx, I'll add both of your mods the next time I enter Cora World: TTF w/ Apotheosis (1.21.1) and I'll see if these fixes has done the trick!
Which could be a few months from now unfortunately, since that world's in rotation along with my 1.20.1 worlds and an upcoming 1.21.1 world for Advent of Ascension 1.21.1 NeoForge. (hopefully porting my AoA 1.20.1 forge world to 1.21.1 Neoforge without issues, could make a backup before entering said world but would just make a new world in 1.21.1 instead of porting my 1.20.1 world if things does go wrong)

this is now fixed in the Apotheosis 8.4.0

Nice, just got the email notification now (as I was lookin through my emails), I'll try them out in two weeks from now (especially since my TTF w/ Aphoseosis mod list is obviously outdated by several months by now...lol)