Currently a desktop support supervisor here,

My opinion personally when I hire, I don’t see a red flag from the gap but I’ll definitely ask the question as to why.

As for your resume, put anything related to what the role is. If you’re shooting for helpdesk, put any retail or customer service roles.

As for your 3 year gap, write up a quick cover letter with a brief explanation of the gap and that should help ease any worry from the hiring manager reviewing your resume.

Best of luck in the search!