Patterns that still have space
Almost every single word is taken. What is still open are pairings: word plus mood (velvetnoir), word plus suffix (petalcore), prefix plus word (itsatlas), and word plus dot separator (soft.archive). The username generator on this site builds all four patterns from any keyword you type.
Keep it typable
Avoid stacked underscores and repeated letters — people mistype them, and mistyped handles cost you tags. Two syllables plus one separator is the sweet spot.
Match the handle to your bio
If your handle is soft and lowercase, your bio should be too. Consistency between handle, name field and bio font is what makes a small profile look professional.