This mod is not for Fabric, but this mod by Carlettos1 is close enough to be considered a Fabric port.

This mod adds some new blocks, slabs, stairs and walls to the game. It is for Minecraft Forge 1.15.2-26.1.2.

The mod adds:

The polished bricks can be crafted with four polished blocks in a 2x2 crafting grid. One polished or unpolished block can be turned into a polished brick or one of its variants using the stonecutter.

The slabs can be crafted with three of the slabs' material in a slab shape in the crafting grid. One piece of the slabs' material or stairs variant can be turned into two slabs using the stonecutter.

The stairs can be crafted with six of the stairs' material in a stairs shape in the crafting grid. One piece of the stairs' material can be turned into a block of stairs using the stonecutter.

The walls can be crafted with six of the wall's material in a trapdoor shape in the crafting grid. One piece of the wall's material can be turned into a wall using the stonecutter.

There are invisible advancements that unlock recipes when you get them.

Mod showcases by NeonSlice:

1.0.0: https://www.youtube.com/watch?v=XT8kIYIrJSs

1.1.0: https://www.youtube.com/watch?v=Csh2JYxJr7c

FAQ

Q: Are there plans to add slabs, stairs and walls for concrete/wool/terracotta/[insert block here]?

A: First of all, thanks for the suggestion! I really appreciate getting suggestions from the community. However, for several reasons, including trying to only add blocks that feel like they could be added by Mojang, I have a few rules for what blocks get variants in this mod, so before you suggest something, please make sure you read and understand them. They are as follows:

• The block must be full (16x16x16), solid, and opaque. This should be obvious; only building blocks get building variants.
• The block must be mineable and obtainable with any pickaxe and only with any pickaxe. Apart from the wooden variants, all vanilla blocks with variants disappear when broken without a pickaxe and drop themselves when broken with any pickaxe.
• The block must not have more than one block state. If the block can be rotated or can otherwise change its texture dynamically, its variants wouldn't look correct in most cases, and therefore wouldn't be the best blocks to build with.
• The block must not have special properties. No vanilla block that has variants emits light or a redstone signal. I guess some of these variants could be useful in some cases, but this mod is all about building, not functionality. This also rules out amethyst blocks for retransmitting vibrations, and lodestones for… well, their obvious function.
• Dyed blocks and blocks with dyed variations will not be getting variants. They just don't feel the same as all the other blocks that have variants. There's probably a reason Mojang has never added them. Besides, there are already multiple mods that add these, and I don't want to add another one to that pile.

Apart from these rules, the blocks I have decided not to add variants for are all the chiseled blocks, since their textures are too intricate and would look weird on non-full block faces, and netherrack, since it feels too soft to be part of a building. To be fair, this is Minecraft, so that shouldn't matter, but still I don't want to add variants for it.

Q: Are there plans to add fences and fence gates for [insert block here]?

A: No. Fences and fence gates were added for nether brick based blocks because there is already such a fence in the game, and for quartz bricks because I guess I just felt like it several years ago. No more will be added.

Q: Can I make the blocks craftable with the Chisel mod?

A: If you want the polished brick blocks to be usable with the Chisel mod for 1.16.5, you can use this datapack: Chisel Tags For New Slabs, Stairs & Walls.zip

Q: Can you add [insert idea here] to the 1.12.2 version?

A: No, I don't update that version anymore.

Q: Some of these questions aren't actually frequently asked!

A: That's not a question.