As for how I use “Created” races, I have a couple home brew versions for my own setting. One of which is the Golmeng, sentient golems with 4 subraces (clay, stone, metal, glass). They were created by Artificers and Wizards that were trying to design golems intelligent enough to complete complex tasks. Eventually they became so smart that they have human-levels of sentience, and were eventually freed of slavery after rebelling against their creators. They now live mostly in harmony with the other races, scattered across the world. I haven’t really delved deep into giving them more interesting lore and plot hooks, but I will eventually.
The second race is the Felshen, a bio-engineered race originally created as the Flesh Golem subraces for the Golmeng, but modified to be more psionically inclined than the rest and to be a true-breeding race. They were made mostly using human and elf DNA, but small bits of other races were used, like Gnomes, Halflings, Dwarves, and Tieflings. The Felshen have innate telepathic powers, and have developed a society that uses psionic magitech for a variety of uses. They use Psi-Gems to extend the rashness of their telepathy, mental libraries to store the collective knowledge of their society, and dream-hubs to allow them to communicate with each other and be productive while sleeping. They are fierce rivals of the Yikkan Goblinoids, masters of magic that believe aberrations use psionics to corrupt the world, and have had dozens of wars and conflicts with them.