In server config, theres configs for what happen with xp when you die.

    #How much experience should players lose when they die?
    #zero is no loss, one is lose everything
    #Range: 0.0 ~ 1.0
    "Loss on death" = 0.5
    #should loss of experience cross levels?
    #for example, if true, a player with 1 xp above their current level would lose the
    #[Loss on death] percentage of xp and fall below their current level.  However,
    #if false, the player would lose only 1 xp as that would put them at the base xp of their current level
    "Lose Levels On Death" = true
    #This setting only matters if [Lose Level On Death] is set to false.
    #If this is true the [Loss On Death] applies only to the experience above the current level
    #for example if level 3 is 1000k xp and the player has 1020 and dies.  the player will only lose
    #the [Loss On Death] of the 20 xp above the level's base.
    "Lose Only Excess" = true

Could be added one new config
1 -> when the xp reachs X% of the level the next time you die, you gonna lose level
Example: if you are 41 and has only 5% of the level already reached, if you die you lose level

And one change
"Lose Only Excess" = true Could work even if "Lose Levels On Death" = true

So with that two, when you lose level (41 -> 40) you gonna lose the same % as said in "Loos on death"

Example with that all
41 with 10% xp, you die -> 41 with 5% xp, you die -> 40 with 95% xp, you die -> 40 with 90% xp

Only with the config thats already exist, its too op losing xp, since is % of all xp
So there 2 options, or you dont lose level or you lose too much

I was able to resolve my issue related to this. So for me, this is no longer necessary, if you want you can remove it

Given how xp changed between 1.20 and 1.21, i'm not writing this twice. I will make this a feature for the 1.21 release.