For some reason, the 1.16.3 version will not allow me to add new blocks. I did the same thing I did in 1.14.2 to add blocks, but the mod doesn't load them.

Any error or just when you enter the world it does not exist in JEI / craftable?

I don't get any error, And the block doesn't exist in jei or crafting.

Below is one default entry, the other two are examples.
{
"baseRegistryName": "minecraft:.*_concrete$",
"depth": 16,
"hardnessMultiplier": 9.0,
"recipeEnabled": true
},
{
"baseRegistryName": "biomesoplenty:fir_log",
"depth": 16,
"hardnessMultiplier": 9.0,
"recipeEnabled": true
},
{
"baseRegistryName": "biomesoplenty:fir_planks",
"depth": 16,
"hardnessMultiplier": 9.0,
"recipeEnabled": true
}

your issue is being looked at as we check all cases [moddedblocks/vanilla, solid/partial, dumb/entity etc.] as well as recent forge changes that may be causing your specific issue. until we have it fully narrowed down dont expect a reply.

CJ generally commits fixes within 7-30 days, and will post here when a fix exists

hello?

Forge changed mod loading again, so my old workaround no longer works. Mods that load before this mod will work fine, but if it ends up loading after it wont.

Still trying to find a way to fix this without having to remove features.

Seem my original hacky idea would work. Was just missing one additional piece so ended up taking many more hours then I expected.