Style Influencer Board

You need to get the Digitalistic Sketchpad for your Sim (I think they might get that one on joining the career, but don't take my word for it).
On it, you have a special interaction to do a Quick Sketch Impression.
Once your Sim does this, they'll get a moodlet. While you have this moodlet, you can Add Impression to the style board, which will add things onto the board until it's full.

Thank you, @darrenfroggy . I haven't received the sketchpad so will see if I can buy one.

You don't even need the sketchpad, you just need to be able to get the correct Inspired moodlet, usually from doing artistic things or possible fashion-related interactions on the computer or when talking to Sims. The current sim in my avatar is a style influencer and currently they own no sketchpads but is able to post impressions on the board just from taking photos on their phone.

Thanks @paradiseplanet . I bought a sketchpad but good to know there are other ways.