You're in a good position legally because you already have demand - that's the hardest part. The most straightforward way right now is to start small, like selling to friends and acquaintances on Instagram while you learn how an actual store works. Post a photo of your work in stories, comment the price, put your Pix in your bio and you're done. This gives you experience with packaging, how to take decent product photos, how to handle delivery, all without spending a dime. Most people just want to know they can pay and receive quickly, they don't care if it's a giant platform or not.
Once you've sold like 20, 30 pieces (or a few months of that), then you can feel out whether it's worth using Shopee, Mercado Livre or creating a link on Linktree with prices. But here's a detail people haven't mentioned: test different types of art, different prices and different audiences before you lock yourself into anywhere. Maybe your watercolors sell better on Instagram with a more creative audience, while book illustration-style drawings might work better on a marketplace. You only figure it out by doing it.
A really practical hack: create a WhatsApp group just to alert your clients about new work. Sounds silly, but that builds a community and recurring traffic that no big platform gives you. And if at some point this grows and becomes real income, then you invest in a better storefront - but while you're starting out, focus on selling to people who already want it, not on setting up infrastructure nobody's using yet.