Litematica file versions for 1.21+ have been found to contain a Remote Code Execution Exploit, allowing malicious code to be executed on your computer in multiplayer servers. Fortunately, it is unlikely that there is a significant risk as this issue has existed since the release of 1.21 and has recently been discovered. Just to be safe, please update the modpack as soon as possible.
If you're updating the modpack from a previous Minecraft version please remove all mods from the mods folder before updating. If you encounter any problems feel free to ask in the discord.