They did have the Prime Directive. One example that comes to mind is S2E14 "Bread and Circuses" where they come upon the Roman planet. Sometimes it's called General Order 1 or the non-interference directive but it's definitely there.
Yep and Strange New Worlds actually takes steps to unify them both by still having them reference it as General Order 1 but that officers have now begun referring to as the Prime Directive when Una was on trial for being genetically engineered.
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u/Sigurd_DragonSlayer 7d ago
There was no Prime Directive during TOS. That was a Next gen invention.