Minecraft version: 1.8.9
Inventory tweaks version: 1.60
One thing, yes, i am still playing 1.8.9. My question is simple. I have the problem that my pickaxe are being sorted wrong, and i could not find anything in the documentation on how to fix this. I want my picks to be sorted from lowest durability to highest, lowest in my Hotbar so i can use them up. I tried multiple things and nothing helped.

This already exists. It's the same way you sort the colours of wool and dye.

<sexyWools>
  <magentaWool id="wool" damage="2" />
  <pinkWool id="wool" damage="6" />
  <purpleWool id="wool" damage="10" />
</sexyWools>

The annoying thing is you'd have to put each individual item separately by damage.

<woodSword>
  <woodSword0 id="woodSword" damage="0"/>
  <woodSword1 id="woodSword" damage="1"/>
  <woodSword2 id="woodSword" damage="2"/>
  <woodSword3 id="woodSword" damage="3"/>
  <woodSword4 id="woodSword" damage="4"/>
  <woodSword5 id="woodSword" damage="5"/>
  <woodSword6 id="woodSword" damage="6"/>
  <woodSword7 id="woodSword" damage="7"/>
  <woodSword8 id="woodSword" damage="8"/>
  <woodSword9 id="woodSword" damage="9"/>
  <woodSword10 id="woodSword" damage="10"/>
</woodSword>

Check your config file for a setting called invertToolDamageSorting.
It seems it was implemented in 1.8, https://minecraft.curseforge.com/projects/inventory-tweaks/files?page=4 for #224

This is not a problem per se, this is how the mod is configured. I have read every documentation possible and this is simply how it works. However, I would also very much enjoy to use lowest durability tools first! So I would recommend that this were either configurable or made possible by a rule.