I have no idea what this mod is or where to find it. I've searched and can't find any mention of it.

I am using 1.13.21-dev, 1.13.21-sources-dev and 1.19.3_HD_U_I2_pre5.

I have also tried using all the other variants of Optifabric. 1.13.21 just crashes on launch. I have tried without the sources and got the same result.

What mods are you using? Please provide the versions for each one of them. Also do not use any version of Optifabric that ends with dev or sources

Do not use -dev.jar. if you use 1.13.21.jar, that message should be disappeared.

Do not use -dev.jar. if you use 1.13.21.jar, that message should be disappeared.

Ok. I tried that and the game did load with only those mods, but it looks like it's not compatible with the Fabric API (as previously reported, I am seeing). I will just have to wait until those issues are resolved as I need the API for the other mods I am using.

Thank you for your assistance