ProgressiveInventory

Mod i remade from yyzsbackpack by yyz729.

Functionality:
Adds 54 locked slots for each player, and each slot is unlocking by completing 5 (default) achivements (if you play vanilla mc with no mods that adding achievements, you can change this value to 2, for example [you can calculate needed value by yourself - divide total number of achievements (vanilla java 1.21.1 has 126) by 54 and floor that value to integer]).

Configuration (config/progressive-inventory.toml):

#What happens to your items in progressive inventory after death. Default means using keepInventory gamerule behaviour.  
#Allowed Values: DEFAULT, DROP, SAVE  
keepItemsAfterDeath = "DEFAULT"  
#How many advancements player should complete to unlock 1 slot (out of 54 total slots)  
\# Default: 5  
\# Range: 1 ~ 100  
advancementsPerSlot = 5

If you set keepItemsAfterDeath to SAVE, items will not drop from player after death, even if keepInventory gamerule is disabled.