Your display name does the introducing
On X the display name appears in bold beside every post, reply and repost, above a handle that can only be 15 characters. With so little room in the handle, the display name is where you can say who you are and what you post.
Describe the account in the form ("weekly threads on personal finance for freelancers") and the AI suggests display names that pair a name with that topic.
Fitting the name to the profile
Your profile has a 1500 x 500 header and a bio of up to 160 characters, so the name doesn't have to say everything. Keep the descriptor short and put the details in the bio.
Then choose a handle that people can connect to the name. If the display name is "Freelance Money Notes", a handle like @freelancemoney is easier to remember than one that shares no words with it.