I have true in Minecraft / gamerule keepinventory true and on the top I keep the things but when I die in the Nether I lose the things and ask myself why? Can you help me?
Have you ever tried putting the gamerule back while in the Nether?
Gamerules are single for each dimension. Nether is a different dimension than the upper world.
Not correct.
Gamerules are for the whole world, including Nether and End.
Do you happen to be on a server? Seems to be a bug from Sponge / Spigot-powered servers.
Normally GameRules apply to the whole world, including Nether and End. (I've just tested in SinglePlayer.)
In your case, you have to reset the gamerule due to the bug in each dimension.
Note: The I on keepInventory must be capitalized. I think there's your mistake. In your question, you wrote it in lowercase.
Is called:
Go to the Nether and type "/ gamerule keepInventory true".
Then that's new. And maybe he plays on an older version or on a server.
Habs tested in 1.8 and 1.14.
In addition, I've been playing since 2011 and I'm 100% sure that gamerules are world-related since they exist.
And yet there are so many possibilities why it is obviously not the case with him.
Server halt.
He also writes that he retains his inventory in the overworld. So your 100% certainty does not seem to be that 100%.
Because he typed the command right there and in the Nether not at all or wrong.
The server running Minecraft seems to be modified, so it's not world-related.
My 100% security related to unmodified servers - because gamerules are always world-related.