ModExtraAssets is no longer getting updated for classic. However, since 2024 there's a MEA Revamped version that fits BepInEx moddding BB+ perfectly!
Just add that line to the loading standards in WarningScreenScript
ModExtraAssets.CreateMaterial(ModExtraAssets.Get<Texture2D>("MY_TEXTURE_NAME"));
yield return new WaitForSeconds(0.01f);
Go to references and find it, then read