They invest in professional designers.
Your looking at their end result without consideration of how long it took them to get there ..versus.. where you are now from a starting position and trying to get there without a similar investment.
Don’t do that , it’s a silly trap.
Do you want to become a web designer , or do you want to run your current business?
but typically just has basic intro to designing Shopify stores
Learning web design has nothing inherently to do with Shopify.
design an aesthetic store?
Just look for art and professional web design courses plenty of those.
Learning and creating aesthetic comes from experience; no shortcuts.
Or is this something I’ll need to learn HTML
And CSS, and Javascript, and Photoshop, and typography and layout and UX and accessibility and frameworks and.. and.. etc.
Recognize when you are trying to bite off more than you can chew.
For basic changes to shopify themes with simple approachable HTML or JS there are plenty of tutorials and example code to be found by searching the question with the specific theme name.
Anything more advanced you need to decided where you want to burn your money/time.
For moderate/advanced stuff like this if you want to burn time learning to do it just search it with CSS as the keyword:
https://www.google.com/search?q=CSS+change+the+font+in+every+letter+of+a+word