Lithium Version :
lithium-neoforge-0.14.0-snapshot+mc1.21.1-build.88.jar

Arclight version :
诸王 (Feudal Kings) / arclight-1.21.1-1.0.0-SNAPSHOT-78c1bfe

OS & Java versions :
CasaOS [Crafty] (Debian) java version 21.0.3

Summary :
It has been observed that the Arclight 1.21.1 with commit (78c1bfe) crashes on boot with Lithium mod installed (NeoForge). It has been confirmed that the issue is not occuring on standalone NeoForge (Version 21.1.73) and with Lithium mod disabled. Please note that the same ticket has been made on Arclight bug tracker with Id [#1535](https://github.com/IzzelAliz/Arclight/issues/1535)

Step to reproduce :

1. Install Arclight 1.21.1 with commit (78c1bfe
2. Install Lithium mod version 0.14.0
3. Run the server
4. Observe the issue.

Possible workaround:
Add the line mixin.ai.poi.fast_portals=false to the lithium.properties file in the config folder.
Please report back if this works around the issue.

Yes, with the dvar mixin.ai.poi.fast_portals=false added to the lithium.properties, the issue no longer occurs on linked versions of Lithium mod and Arclight server.
Thank you very much.

@2No2Name Should I close the ticket as workaround is working or there is any further work planned on this issue ?

I hope the author of arclight server will disable the setting for all users as described here:
https://github.com/CaffeineMC/lithium-fabric/wiki/Disabling-Lithium's-Mixins-using-your-mod's-fabric.mod.json-or-neoforge.mods.toml

Maybe there is a way to get proper compatibility without disabling the setting. But I haven't looked at what arclight server actually does