Redesign the creative inventory, putting everything in different tabs, but with a specific feature inspired by Legacy Console Edition's potion tab:
Only show one of each block type, but have buttons to show different blocks for each type. For example, it wouldn't show all the variants of stone, deepslate, granite, diorite, and other stone types, only the normal ones. But if you select "Cracked Bricks" on the toggle, it would show only the cracked brick variants of each, with an empty slot or red X for the types that don't have a cracked brick variant.
Do this with toggles for wood types, all 16 colors including colorless, ores, armor trims when 1.20 comes out, (the toggle for armor trims should apply to the smithing template as well as the armor) potion upgrades, and anything you can. If you can, add collapsible things like in Bedrock edition. Also, if you can, make a custom banner and firework designer.
While I expect it to support custom tabs from other mods, I would like Create Mod building blocks to be specially supported if you can so I actually get, for example, the modded granite bricks on the granite slot when I select "bricks".
If you make this, I can't thank you enough! The overwhelming amount of blocks is really annoying, and displaying them as if they were variants instead of separate blocks would be a huge help.