PSA: You're intended to be counterplaying champions who have true damage, not counterbuying them
If riot wanted you to be able to stack stats and ignore these champions who have true damage, they wouldn't be giving the true damage. Everyone of them has ways to counterplay them that are more interactive than clicking buttons in the shop window. Try using those if you are having trouble against true damage.
I understand that getting better at positioning, teamwork, mechanics, etc. is much more difficult than buying items that allow you to ignore people, but that's what riot wants you to do so in the long run its better if you get used to the idea. On the upside, these skills will help you against non true damage champions too.
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You can kite them, and their true damage isn't so out of hand since they will have to forgo tank items to increase their damage.
) or true damage that doesn't need offensive stats (
) are problematic.
Vayne's true damage isn't avoidable for most champions. If you can do damage to her, she can do damage back to you unless you're a long range mage such as Viktor, Xerath, or Azir.
Of course, assassins can try to burst her down, but Vayne has insanely powerful self peel to keep them at bay.