In 1.21.10.21 Preview changelog said:
"stone_block_slab4" block is now split into unique instances "mossy_stone_brick_slab", "smooth_quartz_slab", "normal_stone_slab", "cut_sandstone_slab" and "cut_red_sandstone_slab"
However, Stone Slab using incorrect block ID. This is causing existing stone_slab ID does not change to the correct block currently (using /give @s stone_slab gives Smooth Stone Slab)
Linked issues
Attachments
Comments 2

Thank you for your report!
After consideration, the issue is being closed as Working as Intended.
Please note, that mechanics of the game may change between updates.
Things such as graphics, sounds, world creation, biomes, redstone, villagers, and animals may not work the same in current versions.
Full Version History – Snapshot Version History – Feature Requests and Suggestions
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support (Technical Issues) – 📧 Microsoft Support (Account Issues)
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki