Do you have that one friend who keeps dying on your server, and keeps asking for keepInventory to be turned on, which you would gladly do... that is, if it wasn't forced on the rest of your players, none of whom want it?
Individual Keep Inventory is a Fabric mod for making keepInventory work on an individual basis.
The vanilla /gamerule keepInventory command does (or should do) absolutely nothing with this mod, whether it be true or false.
To control the mod to your liking:
/ikeepinv set <username> <true/false> will change a player's individual inventory state, with the default being false.
/ikeepinv get <username> shows you a player's current inventory state.
/ikeepinv default <true/false> will change the default inventory state for new players, set to false by default.
Individual Keep Inventory is completely server-side, meaning vanilla clients should have no issue joining servers with it installed.
Please do submit any feature requests or issues to the Issues page, as this is my first mod.