My game started giving this error on startup:
Failure message: Architectury (architectury) encountered an error while dispatching the net.neoforged.fml.event.lifecycle.FMLCommonSetupEvent event

I didn't add anything new, I just updated five mods: bookshelf, CobbleLoots, Cobblemon Size Variations, Radical Cobble Trainers, and Radical Cobble Trainers API. I'm on 1.21.1 NeoForge 21.1.180 using the latest release of Architectury on Cursed Forge.

Quick update, the mod that requires Architectury is Radical Cobblemon Trainers API, reverting version to [0.12.1-beta] and then Radical Cobblemon Trainers back to version [0.16.0-beta] has stopped all crashes relating to Architectury. Will be reporting this on thier end as well.

This does not work for me! Even removing RCT and RCTAPI I get the same error

Edit: After turning off all of the mods that have architectury as a dependency and turning them on one by one I found the error to be with RCT and RCTAPI as [P4YN-Ki] said but reverting did not work in my case.

Can confirm also started getting this on NeoForge 21.1.180, was previously on 21.1.172 without issues.
Also just Updated a few mods;

CobbleLoots
Radical Cobblemon Trainers
Radical Cobblemon Trainers API

If I keep trying to launch the game, sometimes it actually boots and others I get the same error as the OP.

EDITED to add logs.

Crash Report: https://pastebin.com/nnV1A5CE

I'm going to revert to 21.1.172 and see if the issue persists.

I have the same issue on a cobblemon modpack I have just put together.