In my campaign both goblins and gnomes originated from the same fey faerie folk. When the first of these folk found their way to Midgard (the prime material plane) they found themselves pulled in two directions. One decided to worship Maglubiyet and leaned into the cruel and malicious side of being a sneaky prankster. Gnomes decided to follow Garl Glittergold and embraced the joy and fun associated to their nature.
All gnomes were creative and inventive, some became rock gnomes who love to tinker and invent. Others hearkened back to their fey roots by embracing nature and subterfuge in the way of illusion. Oddly, while both types of gnomes have roughly equal population, many people have never seen a forest gnome community while rock gnome communities are infamous. It's not that people haven't stumbled across forest gnome towns, it's that they pass through or are subtly redirected without ever realizing it.
Meanwhile in rock gnome communities, the gnomes are often in competition with each other trying to earn the title of "Greatest Crafter" with inventions that are sometimes practical but other times lean a bit too much into pizzazz and excitement. People who enter a gnomish city often tell tales of their visit with equal amounts of joy mixed with moments of sheer abject terror akin to riding an extreme roller coaster.
As NPCs both types of gnomes tend to be sages and advisors, but present quite differently. Forest gnomes are calm and gentle, leading you in to a cozy room (watch your head if you're a tallfolk) to have some tea. They'll sit in a comfortable chair as they pull out a pipe and gently ask you how they may assist you. After listening with a furrowed brow, they'll raise their pipe and start blowing bubbles.
A rock gnome? If it's in a human community, you can often get exciting stories from children of the amazing toys and gizmos that get stern looks of consternation from the adults when they aren't secretly smiling at their own memories. The gnome's house will likely decorated with clocks that chime or roar, various devices that may or may not be functional, a clutter of half built and discarded but soon to be recycled objects everywhere. Oh, and tall folk, watch out for the automated flying cobweb remover in case you don't want a haircut.