Can I get sponsored for a UK job from abroad, or do I need to be in the UK first?

Legally, you can absolutely be sponsored from abroad, and many Skilled Worker visas are granted to people who have never set foot in the UK. Practically, it is hard without in-demand skills, because employers usually prefer candidates they can interview and start quickly. It is most realistic in shortage fields like healthcare, engineering and senior tech roles. Apply directly to licensed sponsors, and never pay anyone for a job offer. That is a scam, full stop.