Hey Heart Foam, I've missed your sims Very Much1 <3
Based on my limited experience, several activities (besides Trendi and Livestreaming) will help boost the Entrepreneur skill.
--Activities that my sims have done that definitely boost the Entrepreneur skill (but don't count for Goal Oriented):
*Selling crafted stuff on Plopsy
*Completing Odd Jobs
*Publishing books
*Selling paintings to collector/art gallery (tip from Rhoxi)
--Activities I haven't play-tested but will probably also boost the Entrepreneur skill (but also won't count for Goal Oriented)
*Sales using the vendor table or The Street Gallery (for paintings)
--Freelancer career
This job option didn't show up for my teen.
The HSY pack isn't integrated with base game teen careers, so I've only succeeded in completing the "Reach L3 in a Side Hustle" by maxing the Simfluence or VG Livestreamer career.
Haha, I love the blingy, gold two-screen computer my teen receiving for maxing the Livestreamer career!
I've played teens doing both of the HSY careers and felt that the Livestreamer career was easier.
Please share if your experiences prove differently.
Edited to add: My Not So Berry teen was a Llamacorn Scout but that didn't count for the last Goal Oriented milestone either.
Of course not--it's not a side hustle, haha.
Also, to make extra sure that the task would complete, my teen didn't quit the Livestream career until he completed that "L3 in a side hustle" task.