Getting into threat intel with no prior CTI role — where to start?

Produce intel before anyone pays you to. Pick a threat actor or malware family, track it for a month using open sources, and write structured assessments (with confidence levels and sourcing). That portfolio IS the experience — it shows you can do the analytical work, which is rarer than knowing the jargon. Most junior CTI hires I've seen came in on exactly that kind of self-directed output.