vCard is the file format behind every .vcf attachment your phone has ever offered to import. It is plain text with one field per line, and it is understood natively by iOS, Android, Outlook, Gmail and essentially every address book written in the last two decades. Encode that text into a QR code and you have a business card that works offline, needs no app on either side, and costs nothing to run.
This matters more than it sounds. Most paid digital business card products encode a link to a hosted profile page. That is convenient until the subscription lapses or the vendor shuts the service down, at which point every card you printed becomes a dead link. A vCard QR code carries the actual data, so it keeps working in ten years with no account attached to it.
A working template is already loaded below. Edit the fields to your own details, keep the BEGIN and END lines, and the preview updates as you type. As always the rendering is local, so nothing about your contact details is transmitted to us.