Title says it all. The double slabs look more like concrete. Image below also shows other issue, but it's already on the tracker. I am using some other mods which are listed below.

Additional Structures (by XxRexRaptorxX)
AI Improvements (by QueenOfMissiles)
Alex's Delight (by NCP_Bails)
Alex's Mobs (by sbom_xela)
Allurement (by TeamAbnormals)
AmbientSounds 6 (by CreativeMD)
Anvil Restoration (by Serilum)
AppleSkin (by squeek502)
Architectury API (Fabric/Forge/NeoForge) (by shedaniel)
Armor Statues [Forge & Fabric] (by Fuzs)
Artifacts (by ochotonida)
AttributeFix (by DarkhaxDev)
Autumnity (by TeamAbnormals)
Balm (Forge Edition) (by BlayTheNinth)
Better Advancements (by way2muchnoise)
Better Archeology (by Pandarix)
Better Burning (by DarkhaxDev)
Better chunk loading[Forge/Fabric] (by someaddon)
Better Fps - Render Distance[Forge] (by someaddon)
Better Invisibility (by Purplicious_Cow_)
Better Mods Button [Forge] (by Fuzs)
Better Smithing Table (by jjblock21)
Better Spawner Control (by Serilum)
Better Than Mending (by legobmw99)
Better Third Person (by Socolio)
Better Villages - Forge (by jtl_elisa)
BetterF3 (by cominixo)
Blue Flame Burning (by LobsterJonn)
Blueprint (by TeamAbnormals)
Boatload (by TeamAbnormals)
Bottle Your Xp (by Serilum)
Buzzier Bees (by TeamAbnormals)
Bygone Nether (by izofar)
Caelus API (Forge/NeoForge) (by TheIllusiveC4)
Carpeted Stairs & Slabs (by MehVahdJukaar)
Carry On (by Tschipp)
Catalogue (by MrCrayfish)
Charm of Undying (Fabric/Forge/Quilt) (by TheIllusiveC4)
Cherished Worlds (Fabric/Forge/NeoForge/Quilt) (by TheIllusiveC4)
Citadel (by sbom_xela)
Clickable advancements[Forge/Fabric] (by someaddon)
Cloth Config API (Fabric/Forge/NeoForge) (by shedaniel)
Clumps (by Jaredlll08)
Collective (by Serilum)
Colytra (Fabric/Forge/Quilt) (by TheIllusiveC4)
Comforts (Fabric/Forge/Quilt) (by TheIllusiveC4)
Conduits Prevent Drowned (by Serilum)
Configured (by MrCrayfish)
Configured Defaults [Forge & Fabric] (by Fuzs)
Controlling (by Jaredlll08)
Corail Woodcutter (by Corail_31)
CreativeCore (by CreativeMD)
Crying Portals (by Serilum)
Cupboard (by someaddon)
Curios API (Forge/NeoForge) (by TheIllusiveC4)
Delightful (by brnbrd)
Diagonal Fences [Forge & Fabric] (by Fuzs)
Diagonal Walls (by Fuzs)
Diagonal Windows [Forge & Fabric] (by Fuzs)
Distant Horizons: A Level of Detail mod (by James_Seibel)
Easy Anvils [Forge & Fabric] (by Fuzs)
Extended Slabs + | Now on 1.20.1 (by RealBlackout03)
Farmer's Delight (by vectorwing)
I didn't mean it that way (by LobsterJonn)
Just Enough Archaeology (by LobsterJonn)
Just Enough Items (JEI) (by mezz)
Library Ferret - Forge (by jtl_elisa)
Memory Settings[Forge/Fabric] (by someaddon)
Moonlight Lib (by MehVahdJukaar)
Mouse Tweaks (by YaLTeR)
Polymorph (Fabric/Forge/Quilt) (by TheIllusiveC4)
Puzzles Lib [Forge & Fabric] (by Fuzs)
Searchables (by Jaredlll08)
Server Performance - Smooth Chunk Save[Forge/Fabric] (by someaddon)
YUNG's API (Forge) (by YUNGNICKYOUNG)