I'm not a forge mod developer but I suppose that is either that Modrinth information is wrong about requiring it server-side, or that the mod doesn't report itself correctly as client-side only to forge:

[28Aug2023 21:19:39.106] [Netty Client IO #0/INFO] [net.minecraftforge.client.ForgeHooksClient/CLIENTHOOKS]: Client has mods that are missing on server: [justzoom]

The mod got a full rewrite. If this is still happening, please open a new issue, thank you very much.