When it's done by the state, that's systemic, but it's not systematic. It's systematic when it's done to all trans people (or whoever), not just a few.

(Yes, "all" isn't actually necessary. Some large fraction, though. You can't have a genocide by killing 1% of the people. That's an atrocity, but it's not a genocide.)

Sorry, I apparently didn't read that close enough to notice the systemic/systematic difference.

The UN definition specifically calls out that it doesn't have to be directed at the entire population. It also doesn't make any effort to define any "large fraction" that needs to be met before the definition can be applied. A culling of a percentage of specific population would likely still qualify, but the specifics of these things always varies depending on the context of the specific example being judged. However, it is clear that the UN definition primarily hinges on how people are targeted and the actions that are taken, not the scope.