Patch 1.1.0 for Diablo 4 removes the limit for how many crafting materials can be refined at once at the Alchemist. Prior to the patch, players were only able to refine 20 crafting materials at a time.
Diablo 4 Patch 1.1.0 Patch Notes Alchemist Crafting Overview Farming Crafting Materials
Blizzard
1.1.0a (All Platforms) Build #43333 (PC) and #43223 (Console) – July 18, 2023
There is no longer a limit to how many materials you can refine into higher materials at once.