Is it a mod compatibility issue?

Yes

If it's a mod compatibility issue, please provide the link(s) to the incompatible mod(s)

https://modrinth.com/mod/ars-nouveau/

Minecraft version

1.20.1

Describe the issue

The Ars Nouveau mana system and spellcasting items become non-functional when the player passes through an Immersive Portals-style nether portal, with or without carrying the item in question. As a workaround, I found that passing through a vanilla-style nether portal fixes it (until the next time the player passes through an immersive portal).

Tested in singleplayer; I have no idea what happens in multiplayer.

I know that using Sinytra Connector (and thus, Ars Nouveau) is unsupported with Immersive Portals, so I'm submitting this mainly as an informational "this compat issue exists, here's a workaround" in case anyone else tries the same thing.

tested myself, the workaround for multiplayer is to just rejoin the server or also go thru a regular vanilla portal.

can confirm that this happens for most mods that tie-in directly with the player inventory. in my experience so far, this includes:

• tetra toolbelt access, quick switch do not function and cause clientside desyncs
• sophisticated backpacks hotkey and access do not function and cause clientside desyncs
• weapon master weapons do not function at all

it's likely that most inventory-based effects break completely due to the lack of a proper loading screen because of the seamless nature of the cross-dimensional portals. i wouldn't be surprised if bauble effects and armor effects also break, too!

though as stated above, this is definitely sinytra jank and is easily fixable by reconnecting. just felt i should air this, too, as the issue is technically easily workaroundable but extremely widespread along many mods and quite annoying too